
Class 

Book xi_ 

Copyright^ 

COPYRIGHT DEPOEffi 



Mechanical Drawing 



A Treatise on Technical Drawing as Ex- 
pressed through the Medium of 
the Graphic Language 



BY 



OTHO M. GRAVES 

Assistant Professor of Graphics, Lafayette College 

Author of Orthographic Projection 



EASTON, PA. 

THE CHEMICAL PUBLISHING CO. 

1912 






Copyright, 1912, by Otho M. Graves. 



GCLA327<^3 



PREFACE. 



A course in mechanical drawing should be so designed as to 
awaken the creative faculty of design latent in every student and 
to so train his mechanical execution that he may correctly express 
his thoughts through the medium of the graphic language. The 
power to form a mental image of any proposed design and to 
represent the object on paper by the necessary views or, con- 
versely, to mentally visualize an object by an examination of 
the views representing it, is essential to every successful engi- 
neer. The training of this technical imagination of the student 
should receive careful attention throughout any well planned 
course in Mechanical Drawing. The student should be brought 
to understand that Mechanical Drawing, so called, is in reality a 
graphic language with its own alphabet, grammar, and idioms 
which is to be used as a vehicle of graphic expression. The copy- 
ing of a set of plates, complete in every detail, while affording 
practice in the use of instruments and illustrating various stand- 
ards of execution, is otherwise valueless. A knowledge of the 
graphic language can no more be gained in this way, than one 
could become familiar with any other foreign language by merely 
copying page after page of printed text. 

Xo language can be properly written until the grammar is 
mastered, nor should working drawings be attempted until ortho- 
graphic projection, the grammar of the graphic language, has 
been carefully studied. In the treatment of orthographic pro- 
jection it would seem obvious that concrete objects, such as solids 
of various forms, should be first considered before dealing with 
the more abstruse points and lines. The truth of this state- 
ment has been unquestionably proven by the experience of 
many teachers. 

In the appendix at the rear of this book is a suggested course 
in Mechanical Drawing including twenty-two plates The pur- 
pose of the earlier plates is to familiarize the student with the 
uses of the various instruments and to train his mechanical ex- 



PREFACE IV 

ecution. Yet even in these elementary plates an increasing 
amount of original planning is left to the student subject to the 
supervision of an instructor. As the plates progress a greater 
demand is made upon the power of visualizing objects of three 
dimensions. Those plates which demand a knowledge of ortho- 
graphic projection are so arranged as to permit the instructor to 
assign problems of differing data to students working at adjacent 
tables. 

One hour a week may well be spent in class room recitations 
or lectures. If desired, free hand sketches of assigned models 
may be made by the student as home work and presented at the 
recitation period for examination and discussion. 

The drawing plates of this text should be completed in a col- 
lege year in which two two-hour periods per week — or an equiva- 
lent amount of time- — are devoted to drawing. The theory may 
be cared for in one one-hour recitation per week throughout the 
year. The Lettering plates outlined in Chapter III should be 
completed in twenty one-hour periods. 

Grateful appreciation is due to Mr. M. Berry Doub, Instructor 
in Graphics, Lafayette College, for valuable aid in connection 
with the preparation of this text, and to Messrs. Kielman '14, 
Reside '14, and Ellis '15. students in Lafayette College, for their 
assistance in preparing the illustrations. 

The following firms have been most courteous in supplying 
desired cuts for illustrations: F. Weber and Co., Philadelphia; 
Keuffel & Esser, New York; Dietzgen & Co., Chicago; Kolesch 
and Co., New York; and The Technical Supply Co., of Scranton. 
Pa. 

Easton, Pa., O. M. G. 

September, 19 12. 



CONTENTS. 



Page 

Chapter I. — Instruments and their Use 1-24 

List of Equipment, 1; Instruments, 2; Large Compass, 
3; Large Divider, 6; Bow Pen and Bow Pencil, 7; Bow 
Divider, 9; Ruling Pen, 9; Drawing Board, 11; T Square, 
\2\ Scales, 14; Triangles, 17; Irregular Curves, 20; 
Protractor, 22; Pencils, 22; Ink, 23; Paper, 23; Erasers. 
24; Miscellaneous, 25. 

Chapter II. — General Instructions 26-33 

To Make a Stretch, 26; Penciling, 26; Character of 
Lines, 26; Inking, 28; Symbolic Cross Hatching, 28; 
Tinting, 31; Erasing, 32; Abbreviations, 33. 

Chapter III. — Lettering 35-41 

Purpose, 35; Style, 35; Suggested Course in Lettering, 
37; Composition, 41; Lettering for Architectural De- 
signs and Maps, 41. 

Chapter IV. —Conic Sections 4 2_ 49 

Cone, 42; Cutting Planes, 42; The Circle, 44; The 
Ellipse, 44; The Parabola, 46; The Hyperbola, 47. 

Chapter V. — Orthographic Projection 50-68 

Orthographic Projection, 50; Projection on One Plane. 
50; Projection on Three Planes, 52; Fundamental 
Principles, 54; Sequence of Views, 54; To Obtain the 
Top, Front and Right Side View of a Hollow Cylinder. 
56; To Obtain the Usual Three Views of a Hollow 
Cylinder, 57; To Obtain the Usual Three Views of a 
Cone, 57; To Obtain the Top, Front and Left Side 
Views of the Frustrum of a Cone, 57; To Obtain the 
Top, Front and Right Side Views of a Hexagonal 
Prism, 58; To Obtain the Usual Three Views of a 
Hexagonal Prism, 59; Revolution, 60; Successive 
Revolutions, 62; Oblique Plane of Projection, 67; Sec- 
tional Views, 68. 

Chapter VI. — Working Drawings 79-92 

Clearness, 79; Assembly and Detail Drawings, 80; The 
Number of views Required, 81; Notes, 81; Dimension- 
ing, 81; Title, 84; Checking, 85; Sketching, 86; Shade 
Lines, 88; Line Shading, 89; Structural Drawing, 92. 



VI CONTENTS 

Chapter VII. — Bolts and Screw Threads 95-102 

The Helix, 95; Various Forms of Screw Threads, 96; 
Conventional Representation, 97; Bolt Heads and Nuts, 
98; Set Screws, 101; A Stud Bolt, 102; Machine Screws, 
102; Foundation Bolts. 

Chapter VIII. — Tracings and Prints 103-105 

Tracings, 103; Prints, 104; Sun Frames, 105; Electric 
Printing Machines. 

Appendix.— Suggested Course in Mechanical Drawing. 11 3-1 16 
Time Devoted to Course, 113; Roll Call, 113; Stamping 
Plates, 113; Posting of x\ccepted Plates, 113; Plates Re- 
turned for Correction, 114; Rejected Plates, 114; Time 
of Posting and Returning Plates, 114; Conduct in Draft- 
ing Room, 114; Work Done Outside of Class Hours, 
115; Bulletin Boards, 115; Size of Drawing Plates, 115; 
Instructions Regarding Each Plate, 116 ; Finding 
Plates, 116. 

Plates 1 17-13S 

Plate No. 1, 117; Plate No. 2, 119; Plate No. 3, 120; 
Plate No. 4, 120; Plate No. 5, 122; Plate No. 6, 124; 
Plate No. 7, 124; Plates No. 8 and 9, 126; Plates No. 10 
and n, 126; Plates No. 12 and 13, 127; PlateNo. 14, 127; 
Plate No. 15, 127; Plate No. 16, 128; Plate No. 17, 130; 
Plate No. 18, 132; Plate No. 19, 134; Plate No. 20, 136; 
Plate No. 21, 13S; Plate No. 22, 138. 



CHAPTER I. 

Instruments and their Use. 

I. List of Equipment. — Each man must be provided with the 
following list of equipment, all articles of which are essential. 
This outfit is sufficiently complete for the beginner, but as the 
student gains in experience he will feel the need of useful tools 
not mentioned in this list. Such further tools or instruments 
should be procured as experience indicates and finances permit. 
Any manufacturer is glad to send his catalog upon request, from 
which much valuable information may be obtained both as to 
the care and construction of the instruments already purchased 
and suggestions as to other instruments and devices valuable to 
the draftsman. 

i. Set of drawing instruments of any standard make. The 
set should contain the following instruments : 

Hairspring Compass, S 1 /*", with pen and pencil attach- 
ments and lengthening bar. 

Hairspring Divider, 5". 

Bow Pen, ^/ A " . 

Bow Divider, 3^". 

Ruling Pen, 5^2", with cleaning device. 

Ruling Pen, 4^2", with cleaning device. 

2. Drawing Board, 20" x 28". 

3. T square, 30", with transparent edge. 

4. Triangular boxwood scale. Architect's, or three flat scales. 

5. Triangular boxwood scale, Engineer's, or three flat scales. 

6. 30°-6o° celluloid triangle, 10". 

7. 45 celluloid triangle, 8". 

8. Irregular curve, celluloid. 

9. One bottle black, waterproof, India ink. 
10. Emery pencil pointer, or file. 

II. Ruby pencil eraser. 

12. Ink eraser. 

13. Sponge rubber, or cube of Artgum. 

14. One dozen small thumb tacks. 



2 MECHANICAL DRAWING 

15. Pen holder, three pens Gillott No. 303, and three pens 

Gillott No. 404. 

16. Two 6H pencils, and one 3H. 

17. Medium sized sponge. 

18. Small glass bowl. 

19. One sheet of Whatman's cold pressed paper, 19" x 27" . 

20. One 3 oz. bottle of white paste. 

Assuming the cost of the instruments given in item 1 to be 
$10.00 (which should be regarded as a minimum), the cost of 
the foregoing equipment is about $18.00. 

The purpose and use of the various supplies enumerated in 
Article 1 will now be discussed. 

2. Instruments. — No more serious mistake could be made than 
to imagine that a cheap set of instruments is good enough with 
which to learn to draw, and that a better set may be purchased 
after proficiency has been attained. The cheaper grades of 
instruments begin to show signs of wear in a relatively short 
time. The compasses gradually lose their alignment, the nibs of 
the pens wear unevenly, pivots become loose and screw threads 
worn. Instruments in this condition are a source of annoyance 
and error, and with them even the most experienced draftsman 
would find it difficult to do creditable work. On the other hand 
the life of good instruments is practically unlimited if they are 
used with thoughtful care, and are a constant pleasure to the 
draftsman. It is then, advisable for those men who intend to 
make any branch of engineering their life work to purchase as 
fine instruments as possible. If the state of one's finances pro- 
hibits the purchase of a complete set of the finest grade of instru- 
ments, it might be well to purchase individually as many instru- 
ments as possible at the time, and add to the collection as 
circumstances permit. Eventually such a buyer would be the 
possessor of a set of instruments of which he might well be 
proud. A soft leather case designed to contain any collection of 
instruments will be made to order by any manufacturer of draft- 
ing supplies. Until such a case is desired, the instruments may 
be kept in a piece of chamois folded so that no instrument is 
in contact with another. 



INSTRUMENTS AND THEIR USE 3 

Those men who are pursuing mechanical drawing only tem- 
porarily may reasonably purchase a less expensive set of instru- 
ments. In general, however, a set of instruments as enumerated 
in item i. Art. i, which costs less than $10.00 is expensive at any 
price. 

Nearly all of the well known brands of instruments sold in 
this country are manufactured abroad, notably in Germany and 
Switzerland. The foremost American made instruments are 
those manufactured by Theodore Alteneder & Sons of Philadel- 
phia. These instruments have borne an enviable reputation for 
more than half a century, and many draftsmen consider them to 
be without an equal. 

The Riefler instruments are favorably known abroad and are 
used extensively in the United States. These instruments are of 
unquestioned merit and excellence, and are sold by F. Weber &, 
Co. of Philadelphia. The "Sphinx" instruments, manufactured 
exclusively for the same firm, are acceptable in every way. 

The "Paragon" and "Key Brand" instruments manufactured 
and sold by Keuffel & Esser of New York are worthy of the 
highest praise. This firm has been eminently successful in the 
effort to place the manufacture and sale of drafting supplies in 
general on an honest and reliable foundation. 

Eugene Dietzgen & Co. manufacture and sell the "Gem Union" 
instruments. These instruments have a large sale and are of 
excellent design and workmanship. 

The "T. S. Co." instruments, manufactured for and sold by 
the Technical Supply Co. of Scranton, are favorably known. 

The "Richter" instruments, manufactured in Germany and sold 
by various agents in this country, are worthy of the highest 
praise. 

The "Kern" instruments are a leading Swiss brand. 

Many other instruments are sold in this country and no criti- 
cism of them is intended, but in the opinion of the author the 
ones here named are the best and most reliable. 

3. Large Compass. — The principal material used in the con- 
struction of this instrument is German silver in rolled sheet form. 



4 MECHANICAL, DRAWING 

The nibs of the pen attachment are made of properly tempered 
steel in order to afford the requisite spring. 

Possibly the most important part of the compass is the head 
which forms the joint between the two legs. Unfortunately the 
amateur is unable to ascertain from inspection whether or not 




1 



m 

Sift 



Fig. i. — Tongue joint. 



Fig. 2. — Pivot joint. 



the head is properly constructed, though a poorly constructed 
head is sure to make itself annoyingly obtrusive when in use. 
The surest guide in purchasing is the reputation of the manu- 
facturer and the reliability of the dealer. The tongue joint of 
former years has now given way to the more desirable pivot 




Fig. 3. — Test for alignment. 



joint. In the pivot joint each leg terminates in a disc, the two 

discs being held together in a fork by means of two pivot screws. 

The fork is provided with a handle for convenience in handling. 

All joints and parts should move in the same plane. The test 



INSTRUMENTS AND THEIR USE 5 

for this feature is made by bending the legs outward from the 
head and inward at the knuckle joints, when the points should 
meet exactly. Every good instrument should stand this test. 

The large compass is used for either inking or penciling by 
means of the two attachments. Circles of about n" in diameter 
may be drawn with the $ l / 2 " compass. If a larger diameter is 
desired the lengthening bar must be inserted. 

In order to avoid making large holes in the paper, use that end 
of the needle point which has a shoulder. The needle point 
should be set a little longer than the pen attachment, and kept, 
permanently in this position. When using the pencil attachment 
adjust the lead to suit the needle point. The lead should be 
sharpened to a chisel edge about 3 / 64 " long. The direction of 
the edge of the lead should be tangent to the circle drawn ; other- 
wise a line broader than the edge of the lead would result. 

To set the compass to any desired radius, place two points 
on the drawing paper whose distance apart is equal to the given 
radius. Set the needle point of the compass on one point and, 
spread the other leg until it is approximately over the second 
point. The exact setting is now made by turning the adjusting 
screw which controls the hairspring. 

The compass should be rotated clockwise, with only enough 
downward pressure to keep the needle point in place. Do not 
rotate the compass backward, nor continue the rotation after 
the circle has been completed. When drawing circles of a large 
radius, the knuckle joints should be bent so as to bring the two 
legs perpendicular to the plane of the paper. 

If the circle to be drawn is so large as to require the use of 
the lengthening bar, the leg containing the needle point is steadied 
with the left hand while the pen or pencil point is rotated with- 
the right hand. 

For circles having a radius longer than can be attained by 
the 53/2" compass and lengthening bar, the beam compass is used. 
The needle point and the pen (or pencil) point are placed on two 
separate pieces of metal which are clamped onto a bar of hard 
wood. These bars may be obtained any length from 24" to 60" \ 



6 MECHANICAL DRAWING 

so that a circle may be drawn having a diameter of very nearly 
120". A steel bar is frequently used instead of wood. A beam 
compass of this type is shown in Fig. 4. 




Fig. 4. — Beam compass. 

4. Large Divider. — This instrument is similar in general design 
and construction to the compass except that it has no removable 
parts. It has a two-fold use, first, to transfer dimensions from 
one part of a drawing to another, and second, to divide a line 
into any desired number of equal parts when the divisions cannot 
be readily obtained from the scale. 

To transfer a dimension from one part of a drawing to 
another, set one leg on an end of the dimension to be transferred 
and spread the legs until the other divider point is approximately 
over the other end of the dimension. The exact position of the 
second divider leg may be obtained by means of the set screw' 
controlling the hairspring attachment. The distance between the 
points of the divider legs being equal to the given dimension, this 
distance can be laid off on any desired line. Of course the same 




Fig. 5. — Hairspring divider. 

result could be obtained by scaling the length of the given dimen- 
sion, and laying off the same distance by scale on any other 
desired line. The second method is, however, somewhat more 



INSTRUMENTS AND THEIR USE 



7 



laborious with the possibility of an error through misreading the 
scale. 

To divide a line into a certain number of equal parts, let it 
be desired to divide a line which is about j" long into five equal 
parts. Judging solely by the eye, set the divider points a little 
more than one inch apart and step this distance along the line. 
Suppose that at the last step one leg extends a small amount 
beyond the end of the line. Keep the other leg fixed, and by 
means of the hairspring draw the legs together an amount equal 
to one-fifth the excess. The line should now be re-stepped and 
the process continued until the desired result is exactly attained. 
In stepping off divisions with the dividers, the instrument should 
be rotated in opposite directions at every other step, as though 
describing a series of semi-circles alternately on opposite sides 
of the given line. 

Great care should be taken to avoid pricking holes which are 
needlessly heavy and unsightly. The final points of division 
should be extremely small, yet easily visible. If it is desired to 
save these points for future reference, a light free-hand circle 
should be drawn around each. 

5. Bow Pen and Bow Pencil. — The bow instruments, including 




Fig. 6. — Bow pen. 

pen. pencil, and divider, are made entirely of steel. The legs 
should have a firm outward spring, and are connected by a 




Fig. 7. — Bow pencil. 

threaded bar. The distance between the legs is regulated by a 
thumbnut placed on the threaded bar. The thumbnut may be 



MECHANICAL DRAWING 

placed on the outside of one leg, the legs being held apart, solely 
by their intrinsic spring. Or the thumbnut may be placed 
between the two legs, the connecting bar having a right hand 
thread at one end and a left hand thread at the other end, and 
engaging the legs in swiveling sockets. The advantage of this 
type is that the legs are held rigidly in position without depend- 
ing on the spring. Since the two threads engage simultaneously 
the motion is double that of a single thread, and the legs can be 
set with only one-half the number of turns of the thumbnut, 
which is an added advantage. 

Due to the more rigid construction of the bow instruments, 
circles of small radii can be more accurately drawn than would 
be possible with the large compass. Moreover the radius is 
fixed beyond chance of a change due to an inadvertent pressure 
on the legs. This feature is particularly desirable when drawing 
a number of circles of the same radii. 

The lead of the bow pencil should be brought to a chisel edge 
having a length of about 1 / n2 ", which is nearer a point than in 
the case of the large compass. 

The needle point should project slightly below the pen or 
pencil point. The proper length is such that in drawing a circle 
there is no tendency to lift the needle point from the paper, nor 
the need to unduly force, it into the paper in order to keep the 
moving point in contact with the paper. 

The radius may be rapidly changed and the serviceable life 
of the screw threads be appreciably prolonged, by pressing the 
legs together with one hand, while turning the adjusting screw 
with the fingers of the other hand. 

Circles having a maximum diameter of 2 J A" an d a minimum 




Fig. 8. — Drop pen. 

diameter of about }i" can be drawn with a iVa" bow instrument. 
The "drop pen" or "rivet pen" is a more convenient instrument 



INSTRUMENTS AND THFJR USE O, 

for drawing circles of very small radius than is the bow pen. 
If many such circles are to be drawn, such as rivet and bolt 
holes in structural and machine drawing, and transit stations in 
topographical mapping, this instrument should be included in 
the equipment of the draftsman. 

6. Bow Divider. — The method of use of this instrument is the 
same as for the large divider. It is particularly convenient if 
many divisions are to be made, or if it is desired to keep a certain 
spacing for some time. The setting cannot be changed without 




Fig. 9. — Bow divider. 

intentionally turning the adjusting screw, which precludes the 
possibility of error due to an accidental pressure on the legs 
while the instrument is not in use. 

7. Ruling Pen. — The ruling pen consists of two nibs made of 
properly tempered steel, fastened to a wood or aluminum handle. 
The nibs should be fairly sharp, slightly rounded, and of equal 
length and shape. The two nibs are held together by means of 
a small screw, one nib having a strong outward spring which 
keeps that nib flush against the head of the screw. The distance 
between the nibs is controlled by the screw, thus rendering it 
possible to draw any desired width (frequently called "weight") 
of line. 

The pen is filled by means of the quill attached to the stopper 
of the ink bottle. Do not put too much ink in the pen at one 
time. The ink should not extend upward from the points of 
the nibs more than %.". The danger of overloading the pen is 
that the ink is apt to be shaken from between the nibs, causing 
blots. After filling the pen see that no ink remains on the out- 
side of the nibs. In ruling a line hold the pen almost vertical, 
but with a slight lean to the right. That nib which touches the 
screw head should be on the far side from the ed^e of the T 



io 



MECHANICAL DRAWING 



square or triangle. All lines should be drawn from left to right 
with a free arm movement, making sure that both nibs are in 
constant contact with the paper. If either nib fails to touch the 



ffl 




Fig. io. — Ruling pen with cleaning device, 
paper, by reason of the pen leaning toward or away from the 
draftsman, that edge of the line will be ragged. 

India ink dries rapidly, leaving a slight deposit which if per- 
mitted to remain between the nibs will cause an uneven flow of 
ink and a consequent variation in the width of the line. Hence 
the nibs should be frequently cleaned by drawing between them 
a soft cloth kept for that purpose. Thoroughly clean the pen 




Fig. ii. — Ruling pen with cleaning device, 
before putting it away after the day's work. Most beginners 
are apt to excuse poor work on the ground of a fault in the pen. 
It is far more frequently the case that the pen is not kept suffi- 
ciently clean to allow a uniform flow of the ink. Remember that 
the ink cannot possibly flow if the nibs are screwed together 
until they are in contact. 




Fig. 12.— Detail pen. 

In order to clean the dried ink from between the nibs of the 
pen it is necessary to open the nibs to their full extent. Care 



INSTRUMENTS AND THEIR USE 



II 



must then be taken to carefully reset the nibs to their original 
spacing so that lines drawn before and after cleaning will show 
no variation in width. This need has given rise to several forms 
of "cleaning devices," by which the nibs are automatically re- 
turned to their original positions. Two different forms of this 
device are illustrated in Figs. 10 and 11. 

A double pen is frequently useful for ruling two parallel lines. 
Or a single very broad line can be obtained by filling the space 




Fig. 13. — Double ruling pen. 

between the two pairs of nibs with ink as well as the space be- 
tween each pair of nibs. 

A curve pen set into the handle with a swivel joint is useful 
in drawing curves, contour lines in mapping, etc. 



Fig. 14 — Curve pen with swivel joint. 

The Payzant pen for free hand single stroke lettering is a 
most useful device. 




Fig. 15. — Payzant freehand lettering pen. 

8. Drawing Board. — The drawing board should be made of 
narrow strips of soft pine about one inch thick. The strips 
should be held firmly together by hardwood ledges secured by 
screws in oval slots to allow for contraction and expansion. A 
series of grooves equal in depth to half the thickness of the 
board should be sunk on the under side of the board to prevent 
warping. A hardwood straight edge glued to each end of the 
board is desirable though not essential. The under side of a 
well made board is illustrated in Fig. 16. 



12 MECHANICAL DRAWING 

One of the short edges is made perfectly smooth and even 
and is called the "working edge." This working edge is placed 
to the left to receive the head of the T square. The evenness 
of the working edge is best tested by applying a steel straight 



Fig. 1 6. — Drawing board. 

edge. Or it may be tested as follows : hold the head of the T 1 
square firmly against the working edge and draw a pencil line 
through the center of the paper. Using several points on this 
line as centers, draw arcs of equal radii on each side of the line. 
If the T square be moved along the working edge and can be 
brought tangent to the arcs just drawn, the working edge is per- 
fectly straight. This test assumes that the T square itself is 
accurate. 

It is sometimes convenient to rule lines parallel to the working 
edge by placing the head of the T square against the edge of the 
board nearest the body. This is permissible only when the two 
edges are known to join at an angle of exactly 90 . 

The upper and right hand edges are never used under any 
circumstances. 

9. T Square. — The T square consists of a long, light blade 
rigidly attached at right angles to a head which is about double 
the thickness of the blade. The most accurate and durable T 
squares are made of steel, but the great majority in ordinary use 
are made from woods such as cherry, maple, pear, or ash. The 
two edges of the blade should consist of some transparent mate- 
rial such as celluloid. The transparent edge renders it possible 
to observe the work immediately adjacent to the line being 
drawn, which is very helpful. 



INSTRUMENTS AND THEIR USE 1 3 

An adjustable T square is one which permits the angle between 




Fig. 17. — T Squares with celluoid edges. 




Fig. 18. — T Square with micrometer adjustable head. 




Fig. 19. — T Square with micrometer adjusted protractor head. 

the head and the blade to be regulated as desired. This type of 
T square is convenient though not essential. 



14 MECHANICAL DRAWING 

In Fig. 20 is shown a T square holder which, when attached 
to the end of the blade, holds the T square from slipping by 
pressing against the drawing board. This device is particularly 
useful on a long blade. 




Fig. 20. — T Square holder. 

To use the T square, press the head firmly against the working 
edge of the board with the left hand. Slide the left hand along 
the blade, to hold it firmly in position while drawing the line with 
the right hand. Move the T square up and down the board by 
means of the head. Use only the upper edge of the blade. 

To test the blade for straightness : draw a line the full length 
of the blade. Turn the T square, end for end, and if it can be 
made to coincide with the line already drawn the ruling edge is 
perfectly straight. The same ruling edge must be used, of 
course, in each position of the T square. 

10. Scales. — The two most common materials from which 
scales are made are steel and boxwood. The main advantages 
of the steel scale are its durability and the permanency of its 
deep cut graduations. On the other hand the divisions are diffi- 
cult to read and prove a constant strain on the eyes. For gen- 
eral use the boxwood scale is to be preferred, the edges prefer- 
ably being covered with some white material on which the gradu- 
ations are stamped in black. 

Scales are divided, as regards shape, into two main divisions, 
flat and triangular. The triangular shape has the advantage of 
containing on one scale all of the eleven sets of graduations in 
common use. Its disadvantage is the danger of mistaking the 



INSTRUMENTS AND THEIR USE 



15 



proper scale. A flat scale similar to the one shown in Fig. 23 
and containing four sets of graduations is the most desirable 
form. However, three such scales are needed to contain all of 
the desired graduations. 

In general the representation on paper of an object is neces- 
sarily smaller than the actual size of the object represented. 
The purpose of the scale is to facilitate this required reduction. 
Suppose that it is desired to draw an object one-twelfth of its 
actual size. Then for every twelve inches of the object, one 
inch must be laid off on the drawing; the equivalent expression 
of which is to say that one inch on the drawing is equal to twelve 




Fig. 21. — Triangular boxwood scale, architects'. 




Fig. 22. — Triangular boxwood scale, engineers'. 



inches of the object. The scale to be used is, then, one inch 
equals one foot. If on any straight edge points be set one inch 
apart, the included spaces will represent one foot. If one space 
be now divided into twelve parts, each division will represent 
one inch ; each division may be sub-divided into four parts, each 
sub-division representing one quarter inch. With a scale so 
divided, distances may be laid off such that the resultant draw- 
ing will be one-twelfth the actual size of the object. The evident 
advantage of the scale is that it obviates the necessity of any 
mental division on the part of the draftsman. In Fig. 23 the 
distances i'-o" and io'-io l / 2 " are laid off to a 1" scale. The 
distances 2'-o" and 20' -j" are laid off to a Yi" scale. 



10 



MECHANICAL DRAWING 



The triangular architect's scale contains the following gradua- 
tions which are the ones most frequently used: 

(Full size) 

(One quarter size) 

(One eighth size) 

(One twelfth size) 

(One sixteenth size) 

(One twenty-fourth size) 

(One thirty-second size) 

(One forty-eighth size) 

(One sixty-fourth size) 

(One ninety-sixth size) 

(One one hundred twenty-eighth size) 

A half size scale may be employed by mentally dividing all 
actual dimensions by two, and then using the full size scale. 



12" 


= 1 


-O 


3" 


= 1 


-O 


I/ 2 " 


= 1 


-O 


1' 


= 1 


-O 


Va" 


= 1 


-O 


w 


= 1 


-O 


w 


= 1 


-O 


Va 


— 1 


-O 


'A.' 


=: I 


-O 


%' 


=■1 


-O 


Vs." 


= I 


-O 




Fig. 23. -The use of the scale in laying off dimensions. 

The triangular engineer's scale is divided into ioths, 20ths, 
30ths, 40ths, 50ths, and 6oths of an inch. The engineer's 
scale is used for plotting all work the measurements for which 
were taken in the decimal system. It is particularly valuable 
to the civil engineer in the plotting of maps and surveys. 

Transfer distances directly from the scale to the paper, mark- 
ing the points with a finely pointed lead pencil. Do not set the 
divider or compass legs against the scale graduations and attempt 



INSTRUMENTS AND THEIR USE 



17 



to transfer distances by this means. The method is inaccurate 
and has a disastrous effect on the graduations. 

In laying off a number of equal distances carry the summation 
of distances on the scale. Thus if it be required to lay off 24, 
divisions of }i" each, set the zero of the scale at the starting 
point and, holding the scale fixed, successively lay off y%" , y, 
i}&", i/^", etc. The last point set should fall at the 9" mark, 
which furnishes a valuable check on the work. 

11. Triangles. — Triangles are made of wood, rubber, steel, and 
celluloid. Though the steel triangles are more lastingly accurate 
than those made from any other material, they are not popular 
due to their weight and opaqueness. The celluloid triangles are 
fairly accurate, light, easily handled, transparent, and for gen- 
eral work are to be preferred to those of any other material. 




Fig. 24. — Use of triangles — to obtain angles of 30 , 45 and 6o°. 

It is advantageous to have several sizes of both the 30°-6o° 
and 45 triangles, as it is not convenient to draw large figures 
with small triangles or vice versa. 

As the speed of the draftsman is largely dependent upon his 
facility in the use of triangles in connection with the T square, 
the beginner should at once familiarize himself with their various 
uses, singly and in combination. 



i8 



MECHANICAL DRAWING 



Lines drawn parallel to the blade of the T square are known; 
as horizontal lines. Vertical lines are perpendicular to horizontal 
lines. 

By placing the triangles firmly against the T square blade, 
vertical lines and lines making angles of 30 , 45 °, and 60 ° with 
the horizontal (or vertical) may be drawn. Lines making angles 
of 15 ° and 75 with either the horizontal or vertical may be 




Fig. 25. — Use of triangles — to obtain angles of 15 and 75 . 

drawn by combinations of the two triangles as shown in Fig. 25. 
The student should draw through a point a series of radiating 
lines 1 5 apart from o° to 360 by means of the T square and 
triangle only. 

If it be desired to draw a series of parallel lines which are 
neither horizontal or vertical, place the triangles in conjunction 
and slide one along the other which is held fixed by the left 
hand. 

To test the right angle of either triangle, hold the triangle 
against the T square with the vertical edge at the right and draw 



INSTRUMENTS AND THEIR USE 



19 



a fine vertical line. Reverse the triangle so that the vertical edge 
is at the left. If the vertical edge now coincides with the line 
already drawn the angle is 90°. If the edge and line do not 
coincide they will form an angle one-half of which represents 
the error in the 90 angle of the triangle. If the vertex of the 




c 



Fig. 26. — Use of triangles -to draw parallel and perpendicular lines. 

angle is at the top, the angle of the triangle is greater than 90 ; 
if the vertex is at the bottom the angle of the triangle is less 
than 90 . 

To test the 45 ° triangle, hold the triangle against the T 
square and draw a line along the hypotenuse. Interchange the 
positions of the two acute angles. If the hypotenuse now coin- 
cides with the line already drawn, the angle of the triangle is 
exactly 45 °. If they do not coincide the amount and direction 
of the error is determined as in the preceding paragraph. This 
test is based on the assumption that the 90 angle has already 
been tested and found to be correct. 



20 



MECHANICAL DRAWING 



To test the 6o° triangle ; by means of a protractor or geo- 
metrical construction, draw a line making an angle of 6o° with 
the blade of the T square. Place the short edge of the triangle 
against the T square, and if the hypotenuse then coincides with 
the line already drawn, the 6o° angle of the triangle is correct. 
The 90 angle should have been previously tested. If the 6o° 
and 90 angles are correct the remaining angle must be exactly 
30°. 

The side of a triangle which has been proven inaccurate by 
any of the foregoing methods may be materially improved by a 
judicious application of sand paper. 

12. Irregular Curves are constructed of rubber, wood, and cel- 
luloid, the latter material being preferable. It is frequently desir- 





Fig. 27. — Irregular curves. 



able to make pencil marks on the surface of the curve, hence 
many draftsmen roughen the surface of the celluloid with sand 
paper. The curves are made in a variety of shapes and sizes, 
but for general use the curves of lone radii are most desirable. 



INSTRUMENTS AND THEIR USE 



21 



A varied collection of irregular curves is a valuable part of a 
draftsman's equipment. 

In using an irregular curve do not ink the curved line to the 
full extent of the distance that it apparently matches the irregu- 
lar curve. The importance of this statement can hardly be 
sufficiently emphasized. Let it be required to draw a curved 
line through points a, b, c, d, e, f, g, h, i, j, k, etc. If the curve 
can be fitted from a to / draw the line only as far as e. Now 
fit the curve from d as far as possible, say to i, and draw the 
line from e to h. Fit the curve from g as far as possible, say 
to k, and draw the curve h to /. Proceed in this manner until 
the curve is complete. By this method there are no visible and 
unsightly joints in the curved line. 




Fig. 28. — Protractor, particularly adapted to mapping. 



In drawing a curved line which is symmetrical in respect to 
a given axis, mark with a pencil on the surface of the irregular 
curve the portions used in drawing one-half of the curve, and 
then use the same portions in drawing the other half of the 
curve. By this means the symmetry of the curve is preserved. 
In order to make sure that the two symmetrical halves join one 
another in a smooth curve, it is frequently advisable to stop each 



22 



MECHANICAL DRAWING 



half just short of the axis and use a separate portion of the 
irregular curve for the connection. 

13. Protractor. — A protractor is a device by means of which 
angles of any desired number of degrees may be laid off. It is 
a necessity in nearly all forms of topographical mapping and is 
frequently useful in machine drawing. A simple form of pro- 




Fig. 29. — Protractor, particularly adapted to machine drawing. 

tractor intended for general use and mapping is shown in Fig. 28. 
The protractor shown in Fig. 29 is made of sheet steel with an 
83^2" blade. The vernier reads to five minutes. This form is 
particularly adapted to the requirements of machine drawing. 

14. Pencils. — There are many good brands of pencils on the 
market and an equal number of poor ones. Among the former 
may be mentioned the excellent "Koh-i-Noor" pencils manufac- 
tured by L. & C. Hardmuth and sold by all dealers. The 
"Apollo" pencils manufactured by F. Weber & Co., the 
"Hyperion" pencils of Eugene Dietzgen, Keuffel & Esser's 
"Paragon" pencils, and the "Swan" pencils sold by the Technical 
Supply Co. of Scranton are to be highly recommended. 

The standard gradation of pencils according to the degree of 
hardness of the lead is commonly accepted as. follows: 6B, 5B, 



INSTRUMENTS AND THEIR USE 2$ 

4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H. and 6H. According 
to this notation F and HB are considered medium, the leads 
growing harder through the H's until 6H is reached and softer 
through the Bs until 6B is reached. The degree of hardness 
desired by the draftsman is considerably dependent upon the 
class of work and the grade of paper employed. In general the 
6H pencil is used for line drawing which is to be traced or inked, 
and the 3H pencil for lettering. 

The draftsman should possess two 6H pencils, one of which 
should be brought to a chisel edge as follows : cut away the wood 
for about i%", exposing about y%" of the lead. Flatten the lead 
and bring to a knife edge by rubbing on an Emery pencil pointer 
or file. The other 6H pencil is sharpened to a long conical point 
for the laying off of dimensions. 

Some draftsmen prefer to bring one end of the pencil to a 
chisel point and the other end of the same pencil to a conical 
point. It is claimed that this method saves time, since it is 
quicker to turn the same pencil end for end in laying off a dimen- 
sion, than to lay down one pencil and pick up another. On the 
other side it may be said that the continued sharpening of a 
pencil at both ends rapidly decreases its useful length. At best, 
this is a matter of personal choice and that method should be 
adopted which is best suited to one's own needs. It is impera- 
tive, however, that a 6IT conical pointed lead be kept for no 
other purpose than the laying off of dimensions. 

15. Ink. — One of the best inks manufactured for drafting pur- 
poses is Higgin's Water-proof India Ink. Other excellent inks 
are made by F. \Yeber & Co., Keuffel & Esser and Eugene 
Dietzgen. Inks are made in many colors, though the practice of 
using colored inks on drawings is steadily decreasing. The use 
of colored inks on some forms of mapping is frequently advan- 
tageous. 

16. Paper. — Drawing paper is made in a variety of styles to 
meet a variety of needs. In general, the white papers are in- 
tended for finished or inked drawings, and the cream or buff 
papers for pencilled or detail drawings. In the average drafting 



24 MKCHANICAI, DRAWING 

room by far the greater number of drawings are made in pencil 
on the buff or cream detail paper. These drawings are then 
traced and from the tracing blue prints are obtained ; this process 
will be described later. Many drawings are made, however, 
directly in ink on white paper. Maps, railroad layouts, or any 
other drawings which may have to stand hard use, are made in 
ink on a heavy white paper backed with tough linen. The sur- 
face of such a drawing is sometimes protected by a coat of 
white varnish. 

A paper intended to receive ink should be white, of close firm 
texture, and should neither repel nor unduly absorb liquids. A 
good paper should stand at least four successive erasures of an 
ink line. 

Two papers which meet these requirements are Whatman's 
and F. Weber & Co.'s "Fabriano." These papers are made in 
standard commercial sized sheets, or in 10 to 50 yard rolls, with 
three styles of finishing the surface, hot pressed (smooth), cold 
pressed (medium), and rough (course grained). The cold 
pressed paper is the most serviceable for general use. That side 
of the paper from which the makers water mark can be read is 
regarded as the "right" side. 

17. Erasers.- — For the erasure of pencil lines use a Ruby eraser. 




Fig. 29a. — Erasing shield. 

Ink lines may best be erased by removing only the surface of the 
line with an ink eraser, completing the erasure with a Ruby 
eraser. Under no circumstances should any form of "scrateher" 
or knife blade be used for erasing. 



INSTRUMENTS AND THEIR USE 2$ 

An erasing stencil consisting of a thin piece of metal containing 
holes of various shapes may be used to protect other lines adja- 
cent to the one being erased. 

A soft sponge eraser, or cube of Artgum, is serviceable in 
giving the drawing a general cleaning without erasing any lines. 

18. Miscellaneous. — Thumb tacks are useful for temporarily 
holding the drawing in place or for holding reference notes or 
sketches to the board. 

If the paper is not to be stretched and the margins pasted 
down, it should be held in place by one-ounce iron tacks. These 
tacks can be pushed into the board until their heads are flush 
with the paper. Such tacks offer no obstacle to the sliding back 
and forth of T square and triangles as do the thumb tacks. 

The pen holder should have a large grip (about y 2 " in diam- 
eter) tapering off into a slender handle. The best material for 
the grip is cork or soft unglazed wood. Gillott's No. 303 and 
No. 404 are excellent pens for medium sized free hand lettering. 

A pen wiper should be kept close at hand and frequently used. 
Chamois or lintless linen are excellent materials for this purpose. 

The sponge, glass bowl, and jar of paste are used in making 
a stretch as described in Art. 19. 



CHAPTER II. 



General Instructions. 

19. To Make a Stretch. — Lay the paper on the drawing board 
and fold upward about y 2 " of each edge. Fill the small glass 
bowl with water and by means of the sponge thoroughly wet the 
exposed surface of the paper taking care not to dampen the 
folded edges. Squeeze all water from the sponge and remove 
all surplus water from the paper by absorbing it with the sponge. 
Spread paste on the inner surfaces of the folded margins. Lift 
the paper from the board and lay the side which has been wet 
next to the board. Paste the margins to the board working from 
the center outward and at the same time smoothing as many 
wrinkles as possible from the paper. The paper should be 
allowed to dry in a horizontal position, and when dry should 
present a smooth surface free from wrinkles with edges firmly 
fastened to the board. 

20. Penciling. — The pencils should be sharpened as stated in 
Art. 14, the 6H being used for the drawing of lines and the 3H 
for lettering. 

In making a line hold the pencil nearly vertical with a slight 
inclination to the right. The chisel point should touch the paper 
about 1 / 32 " away from the straight edge. All lines should be 
cfrawn from left to right and away from the body, even 
though to do this necessitates the turning of the drawing board 
or moving around the drafting table, so that the free and even 
movement of the arm may not be cramped. The lines should 
be very fine which is accomplished only by maintaining a sharp 
edge on the chisel point of the pencil. 

The student should always remember that the three essential 
characteristics of a good draftsman are speed, accuracy and 
neatness. The last two go hand in hand and are of more impor- 
tance than the first. 

21. Character of Lines. — For ease in reading a drawing, various 
kinds of lines are used, each kind expressing to the trained eye 
a certain fixed meaning. Unfortunately there is no universally 



GENERAL INSTRUCTIONS 2J 

accepted standard, but the alphabet of lines shown in Fig. 30 is 
commonly accepted by most draftsmen in this country. 



' V/s/jb/e ouf/ine. 

_ /^i/zs/bfe out/zne^crshesj-" 

/one?, spaces -£ "/o/?y. 

/7//77ens/o/7 //ne. 

Center ///7e_, abs/?es ^"/onc? 

c/ots §-' ' /ony, spaces A'Vor?^ 

. ■ //7c/ef/'/7/te bracr/r //s?e. 

S/?ac/e //he., f-w/ce f/?e weight 

of the ouf/zne. 

Fig. 30. — Character of lines. 

The dimensions given are to be judged solely by the eye. Prac- 
tice so trains the judgment of the eye that these distances can 
be obtained with surprising accuracy. Uniformity in the length 
and spacing of the dots and dashes should be maintained, how- 
ever long the line may be. The otherwise pleasing effect of a 
drawing is easily marred by irregularity in dot and dash lines. 
The same degree of care, in this regard, is not as essential in 
pencil work which is to be inked or traced. 

On inked drawings all the lines shown in Fig. 30 should be 
drawn in black ink. A space is left near the center of dimension 
lines for the insertion of figures. In structural drawing the 
dimension line is continuous and the figures are placed just above 
the line. The use of colored inks for dimension and center lines 
is not desirable as it requires a greater expenditure of time on 
the part of the draftsman, and good prints cannot be made from 
tracings on which colored inks were used. Happily the modern 
practice is to use only black ink on all drawings which are not 
to be colored for display. An interesting inquiry into modern 
drafting room practice, conducted by Prof. Reid of the Armour 
Institute of Technology, shows that only 13 per cent, of one 
hundred firms questioned use colored inks for dimension and 



28 MECHANICAL DRAWING 

center lines. The remaining 87 per cent, use the black line as 
stated above. 

22. Inking. — In general a drawing should be complete in pencil 
before starting the inking. The speed of the inking will be 
greatly increased if some definite system is followed such as the 
one here outlined : 

1. Ink all circles and circular arcs first, beginning with the 

smallest. 

2. Ink all horizontal dotted lines. 

3. Ink all vertical dotted lines. 

4. Ink all other dotted lines. 

5. Ink all horizontal full lines. 

6. Ink all vertical full lines. 

7. Ink all other full lines. 

8. Ink center and dimension lines. 

9. All figures and notes. 

10. All cross hatching. 

11. Title and border. 

In inking horizontal lines, ink those at the top of the drawing 
first, and work downward; in inking vertical lines, ink those at 
the left of the drawing first and work to the right. 

The tendency of the student is to make all lines too light. The 
finest line should be heavy enough to stand out clear and bold to 
the eye. There should be no minute white spaces in the line 
indicating that the nibs of the pen were set so close together as 
to render impossible an even flow of ink. It is advisable to rule 
on scrap paper a standard set of the lines to be used on the 
drawing. These lines may then be referred to when resetting 
the pen after cleaning. This is not so essential if the pen con- 
tains a device which automatically returns the nibs to their origi- 
nal position after cleaning. 

23. Symbolic Cross Hatching. — It is frequently desirable to 
represent an interior view of an object as though it had been 
exposed to view by an imaginary cutting plane, that portion of 
the object between the observer and the cutting plane being 
regarded as removed. Such a view is called a section, and is 



GENERAL INSTRUCTIONS 



29 



indicated on the drawing by covering the area in question with 
parallel straight lines, usually making an angle of 45 ° with the 
horizontal. These lines are called cross hatching. 





^^^co^rr/? j||||| 








Z/f/4^J 






Fig. 31. — Symbolic cross hatching. 

By varying the character and spacing of the lines composing 
the cross hatching various materials may be indicated. There is 
no universally accepted standard of symbolic cross hatching due, 



30 



MECHANICAL DRAWING 



possibly, to the great number of materials used in engineering 
construction. It is advisable, therefore, to plainly letter the 
material in addition to the symbolic cross hatching, the function 
of the latter being only to indicate that different materials are 
used in the given design. The conventional symbols shown in 
Fig. 31 are accepted and used by many draftsmen in this country. 






TIN 



7\ 



^ 



7Ps 



Fig. 31a. — Representation of stone and brick masonry. 

It is to be noted that different materials in the same section 
are best contrasted by sloping the cross hatching in opposite 
directions. 

The spaces between the lines of the cross hatching are judged 
solely by the eye, but care should be taken to maintain uniformity 
of spacing. It is a helpful guide to glance back at the spacing 
of the last four or five lines drawn. Various forms of "section 
liners" are on the market which are merely devices for mechan- 
ically regulating the spacing. Unless a great amount of cross 
hatching is being done their purchase is not to be recommended. 
A home-made device to accomplish the same purpose is shown 



GENERAL INSTRUCTIONS 



31 



in Fig. 32. It is made of thin wood and is used by slipping the 
block and holding the triangle, then holding the triangle and 
slipping the block, etc. One piece of wood will evidently main- 
tain the same spacing and cannot be changed, so that several 
pieces should be kept on hand for various spacings. 




Fig. 32. — Section line device. 

The width of the spaces is largely dependent upon the area 
to be cross hatched and no rule in this connection can be given. 
The tendency of the student, however, is to place the lines too 
close together. 

24. Tinting. — On large drawings it is frequently more advan- 
tageous to distinguish various materials by the use of different 
colored washes, instead of by cross hatching. Tinting is also 
largely used in map drawing to clearly indicate the various divi- 
sions of the map. Architectural drawings are nearly always 
tinted, thereby gaining greatly in beauty and realistic effect. 

The paper should be of good quality and cold pressed. 

The size of the brush should depend somewhat on the area 
to be tinted, sharp turns and small corners demanding a finer 
pointed brush than would a large unbroken area. In any case 
the brush should naturally assume a good point when filled with 
the wash or plain water. 

The wash is prepared by lightly rubbing the moistened brush 
on a cake of color and then stirring the brush in a small porce- 



$2 MECHANICAL DRAWING 

lain or china dish containing water. The wash had best be too 
light in color rather than too dark. The tinted area may easily 
be darkened by applying a second coat of the wash. But if the 
original wash is too dark, it is an extremely difficult task to 
lighten the tinted surface. 

Before applying the wash the board should be inclined at an 
angle of approximately 15 , so as to induce a gentle downward 
flow of the liquid. 

Fill the brush with the wash, and starting at the upper por- 
tion of the drawing apply the wash from left to right in such a. 
quantity as to form a narrow horizontal puddle of the wash. 
Draw this surplus color downward, continuing to work from 
left to right. When the bottom edge is reached, dry the brush 
by pressing between the thumb and forefinger of the left hand, 
and use the brush as a sponge to absorb the surplus wash. Any 
part of the wash which has perchance been drawn outside the 
bounding lines of the figure, should be permitted to thoroughly 
dry before removing with a pencil eraser. 

A graded tint may be secured by applying at the upper edge 
of the area the darkest color desired and drawing the wash 
downward by adding with the brush a gradually increasing quan- 
tity of pure water. 

Since sediment is apt to form in the bottom of the saucer con- 
taining the wash, it is better to touch the brush to the upper 
portion of the wash, not permitting it to touch the bottom of the 
dish. 

25. Erasing. — Pencil lines should be erased by means of a 
Ruby or Emerald eraser. The small particles of rubber caused 
by the erasing should be dusted off with a brush or cloth. The 
palm of the hand, if clean and dry, may also be used for this 
purpose. 

Ink lines should not be erased until thoroughly dry. India ink 
seldom penetrates the surface of good drawing papers. The 
endeavor should be to remove the coating of ink without injur- 
ing the surface of the paper. This is best accomplished by 
disturbing and loosening the coating of ink with an ink eraser, 



GENERAI, INSTRUCTIONS 33 

and finishing the erasure with a pencil eraser. Any form of 
knife edge or scratcher should be used with the greatest care. 
The danger of such a tool is that the surface of the paper may 
be so destroyed as to render it impossible to re-ink over the 
erasure. 

It is frequently desirable to give a drawing, a general cleaning. 
This may be accomplished by lightly rubbing the drawing with 
a sponge rubber or piece of Artgum. Pass over the inked lines 
as lightly as possible as even the softest rubber tends to slightly 
destroy the intense blackness of the ink which is so desirable. 

Many draftsmen satisfactorily clean a drawing by rubbing 
bread crumbs over its surface with the palm of the hand. 

26. Abbreviations. — The following abbreviations are frequently 
used in many drafting rooms : 



Feet or Foot 


Ft., ft., or '. 


Inches or Inch 


In., in., or ". 


Degrees or Degree 


o 


Minutes or Minute 


/ 


Seconds or Second 


" 


Angle 


Z. 


Center to Center 


c to c. 


Pitch 


p. 


Diameter 


Dia. or D. 


Radius 


Rad. or R. 


Circumference 


Circum. 


Hexagonal 


Hex. 


Square 


Sq. 


Threads 


Thds. 


Threads per Inch 


Thds. per In 


Revolutions per Minute 


R. P. M. 


Pounds 


lbs or ±t 



There is far less uniformity of practice as regards the sym- 
bolic meaning of colors to represent various materials, than is 
the case in cross hatching. The following washes are used by 
some large concerns, but are by no means universal : 



34 



MECHANICAL, DRAWING 



Cast Iron 


Payne's Grey 


Wrought Iron 


Russian Blue 


Steel 


3 parts Russian Blue, i part 




Crimson Lake. 


Brass 


Gamboge 


Copper 


4 parts Crimson Lake, I part 




Burnt Sienna 


Lead or Babbitt 


Light India Ink 


Glass 


Light Prussian Blue with line 




shading 


Brick 


Crimson Lake with section 




lines 



Manufacturers of drafting supplies have on the market vari- 
ous colors labelled "Cast Iron," "Steel," "Wood," etc., which 
closely approximate in color the material to be represented. Until 
some standard is authoritatively recommended by the leading en- 
gineering societies and generally adopted by draftsmen, all sec- 
tions should be clearly lettered whether cross hatched or tinted. 



CHAPTER III. 



Lettering. 

27. Purpose. — It is hardly possible to convey on a drawing 
the required information by means of the graphic language of 
lines alone. Such data as the figures representing lengths and 
sizes, explanatory notes, statements as to kind of material, finish, 
number of pieces desired, title, etc., must be lettered. If the 
lettering is to be serviceable it must be neat and legible, and of 
a style that permits rapid execution. 

28. Style. — The style of lettering adopted for working draw- 
ings should possess these three important characteristics, beauty, 
legibility, and ease of execution. If any one of these features 
be lacking the quality of the other two is necessarily depreciated. 

Beauty to the trained, technical eye does not mean ornate 
letters with fancy scrolls and appendages, but rather letters that 
are appropriate to the work in hand and of modest, unassuming 
appearance. The general tone of any drawing is greatly im- 
proved by well executed lettering, and on the other hand poor, 
or inappropriate, lettering spoils the appearance, however well 
the line work be executed. 

Legibility is dependent not only upon the type of the lettering, 
but is even more affected by the spacing of letters and words 
and whether lower case letters or capitals are used. Words are 
read not by spelling out the composing letters, but by familiarity 
with the forms of the words. The body of any written matter, 
be it in long hand, typewritten, or printed, is in lower case letters, 
and hence the eye of the reader has become accustomed to the 
forms of words expressed in lower case letters. It is, then, 
important that all notes on a drawing be stated in lower case 
lettering, reserving the use of capitals for headings requiring 
particular emphasis or titles. Unfortunately some men and some 
systems advocate the use of capitals for all notes. Such prac- 
tice is deplorable and is followed only by a small minority of 
draftsmen. 



2,6 MECHANICAL DRAWING 

Ease of execution depends solely upon the type of lettering. 
Economically any result which is disproportionate to the amount 
of time and energy required in its accomplishment is undesirable. 
No thinking person would tolerate an expenditure of four hours 
in lettering a drawing the rest of whose execution required but 
two hours. Ornate letters composed of tree limbs with clinging 
vines, or isometric block letters casting shadows of questionable 
accuracy, or even so-called mechanical letters laboriously made 
with the ruling pen and bow compass at the expense of the 
nervous system of the draftsman, are when used in ordinary 
drafting, monstrosities which are happily passing into general 
disrepute. Since the primary purpose of lettering a drawing is 
to state additional information, no letters are appropriate which 
detract attention from the drawing itself. The lettering and line 
work should blend into one harmonious whole, and no form of 
lettering which is unduly ornate will fulfill this requirement. 

29. The Reinhardt Letter. — The system of lettering advocated 

fofh /*/ jjy W*/r // tovm '</7?r? 
& o fa p *&f 3 q */* r 3» s rfftytu 
V" v '*\$/*w w x '% y ?zz. 
WA vh 2 B G C *D)-0 #&£ *£f 

3 3 

3* S *T' T *U*U W V rfi^W 

ft X ^fi* K i^Z I2 34S6 789 O 



Fig- 33- — Analysis of the Reinhardt letter, 
by Mr. Charles W. Reinhart, Chief of the Drafting Department 



JITTERING 37 

of the Engineering News and first published by him in 1895, is 
most excellent. Possibly more than anyone else, Mr. Reinhardt 
has purified engineering lettering and placed it on a sane and 
firm foundation. His text book on "Lettering" should be in 
the hands of all draftsmen. In Fig. 33 is shown the Reinhardt 
alphabet with a brief analysis, the arrows indicating the direc- 
tion, and the numbers the sequence of the strokes. For a more 
detailed study of the method of making each letter refer to "Let- 
tering" — C. W. Reinhardt. In the next paragraph a course of 
lettering is suggested based on this book as a text. 

30. Suggested Course in Lettering. — The progress of the stu- 
dent is greatly accelerated if he practices on paper of a suitable 
ruling such as that shown in the following illustrations. 1 The 
pen should be held firmly and yet without undue contraction of 
the fingers. Do not press on the pen point. This statement 
can not be over emphasized and should be constantly borne in 
mind. Pressure on the pen point results in lines of varying 
width, which is far from desirable. Endeavor to keep the slope 
uniform. 

The letters in the following plates are grouped according to 
similarity of construction rather than in the usual alphabetical 
order, the grouping of the lower case letters necessarily differ- 
ing from that of the capitals. 

/////////// A7 
/ / / / / / / / / / , 

/ / / / / / / / / / 

Fig. 34. — Basic strokes in lettering. 



J Sheets of this ruling have been designed by the author and may be se- 
cured of F. Weber and Co., Philadelphia. The over all dimensions are 
8" X r°/^ // . an d inside the border lines, 6 // X 8". 



MECHANICAL DRAWING 






s 



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LETTERING 




o&nsiclergiio.h though frmllfoffaw ind^Gou^so, JLr^ 
Ease hfr hfu ShoulqsHo want v i dent im pro vvnwnt ov&r Th& 

PffimfmStrthata moderates// sKiltful 'fyana f $ w'ded 
TraToyour Thought on the> WorK it] hancf 



Fig. 36. — Lettering done by a student on entering course in lettering. 

/ihe appearance of a drawing/ whose workmanship 
/s otherwise exce/ient, may <6e compiefety ' spoiied Ay 
poor fettering/. //? the pracficaf drafting room the 
draftsman who fetters neatfy and rapidty is regarded 
as more vaiuahfe than or?e w/?ose ietfering /j mediocre. 
The engineering student shoufd master a <styfe of ie tiering 
which possesses these /'/free important" features; beauty, 
/egib/fty a/r?d ease of execution. 7his car? he accompiish- 
ea 0/7/y 6y a carefui study of the form ana" method of 
producing each ietter-, combined with thoughtfui prac- 
tice. After proficiency has heer? attained in the execu- 
tion of the individuai tetters, the attention shou/d be 
devoted to composition /n order- /-/pat practice may he 
had in the spacing of fetters in words r and words in 
sentences, the proper spacing is de/oendent soieiy 
upon the taste and iudgement of the draftsman. 

7he student shot/ id endeai/or to maintain a uniform 
s/ant to the tetters, and to permit no variation /n the 
weight of the individual tines. A moderate fy striff- 
fuif hand guided with thoughtful care, /s a more effici- 
ent combination than unusual sir ill and thoughtiess execution. 

Fig« 37- — Lettering done by same student after devoting two hours 
per week for 12 weeks to lettering. 



40 MECHANICAL DRAWING 



Lower Case Letters. 



Plate I consists of the practice strokes shown in Fig. 34. These 
strokes form the basis of lettering of this character. 

Plate II is composed of the letters h, i, j, 1, and t. This plate 
is shown in full in Fig. 35. It will be noted that each letter is 
given a full line, the lines of letters alternating in the order 
stated. The following plates are to be treated similarly. 

Plate III contains the letters r, k, x, f , y and z. 

Plate IV is composed of the letters n, m, u, v and w. 

Plate V consists of the letters o, a, e, c and s. 

Plate VI contains the letters b, p, d, g and q. 

Capital Letters. 

Plate VII consists of the letters I, L,, F, E and H. 

Plate VIII is composed of the letters V, A, K, W, X and Z. 

Plate IX contains the letters Y, T, N, M and J. 

Plate X consists of the letters U, P, R, D and B. 

Plate XI is composed of the letters C, G, O, Q and S. 

Numerals. 

Plate XII contains the numerals 1, 7, 4, 3 and 2. 
Plate XIII consists of the numerals 5, 6, 9, o, 8. 

Composition. 

Plate XIV is a copy of the plate shown in Fig. 37. 

An interesting record of progress showing the benefit derived 
from the course may be obtained by having the student on enter- 
ing the course immediately copy this plate without the slightest 
help or instruction. A comparison of this first plate with Plate 
XIV is apt to show almost astonishing improvement. Fig. 36 is 
the actual reproduction of a beginner's first attempt, and Fig. 37 
was executed by the same man three months later. 

These two plates are fairly typical of the improvement shown 
in hundreds of similar tests observed by the author. 

Plate XV may consist of any work designated by the instruc- 
tor such as a title or further work in composition. 



LETTERING 4 1 

This course may be supplemented, if time permits, by a study 
of vertical lettering. Vertical letters are possibly somewhat 
clearer than the sloping, but require a longer time in execution, 
and for general utility are not to be recommended. 

31. Composition. — The spacing of letters in words and the 
spacing of words in sentences is quite as important as the forma- 
tion of the individual letters. The proper spacing is almost en- 
tirely dependent upon the artistic taste of the draftsman. In 
general keep the letters of a word fairly close together with the 
white spaces between each letter of uniform size and the spacing 
between the words equal to about the height of the letter. The 
judgment and taste of the draftsman are increased with prac- 
tice, and after the execution of the individual letters has been 
mastered, considerable attention should be devoted to composi- 
tion. The student can gain greatly in proficiency by using odd 
minutes to letter original statements of any kind. 

32. Lettering for Architectural Designs and Maps. — The letter- 
ing used on these classes of work is permissibly more ornate than 
would be deemed advisable in machine or structural drawing, 
and a draftsman who desires more versitality in his lettering 
should perfect himself in styles of lettering other than the one 
treated in this chapter. For such study the student is referred 
to the admirable text. ''The Essentials of Lettering," by Profes- 
sors French and Meiklehohn. In this book useful alphabets are 
analyzed which have greater beauty and are more adaptable to 
Architectural and Topographical drawing than the Reinhardt 
letter. This text is of as great service to the practicing drafts- 
man as to the college student who has completed a course in the 
Reinhardt system. 



CHAPTER IV. 



Conic Sections. 

33. Cone. — A cone is a solid generated by a right line moving 
so as constantly to touch a closed curve and pass through a 
fixed point not in the same plane with the curve. The succes- 
sive positions of the generating line are elements of the cone and 
the fixed point is the vertex. The plane of the closed curve is 
the base of the cone. If the closed curve is a circle the cone is 




Sarss 



Fig. 38. — Cone. 

a circular cone. A line drawn through the vertex to the centre 
of the base is the axis, and the length of the axis is known as the 
altitude. If the axis is perpendicular to the base the cone is a 
right cone. 

It is obvious that in a right circular cone all the elements make 
the same angle with the axis. 

34. Cutting Planes. — A right circular cone may be cut by planes 
at different angles so as to obtain four distinct curves, called 
conic sections, as follows; a plane perpendicular to the axis cuts 
a circle, a plane making a greater angle with the axis than do 
the elements cuts an ellipse, a plane making the same angle with 
the axis as do the elements cuts a parabola, and finally a plane 
making a smaller angle with the axis than do the elements cuts 



CONIC SECTIONS 



43 



an hyperbola. No curves other than these can be cut from a 
cone by a plane. 




C/'rc/e 





£///'pse 



/^cyraSo/a 




//y/>er/6o/cr 



Fig- 39- — Conic sections. 

These four curves can be drawn by actually determining the 
curve cut from the cone by any plane, or by plotting a series of 
points according to the law known to govern the generation of 
each curve. Only the latter method will be treated in this chap- 
ter. 



44 



MECHANICAL DRAWING 



35. The Circle. — A circle is generated by a point moving in a 
plane and remaining at a constant distance from a fixed point 
called the center. The compass is a mechanical device for the 
drawing of circles and no further discussion of this curve is 
needed. 

36. The Ellipse. — An ellipse is generated by a point moving in 
a plane so that the sum of its distances from two fixed points, 
called foci, remains constant. 

To Construct an Ellipse. First Method. 
Given: The major and minor axes. In Fig. 40 let AA X and 
BB X be the major and minor axes, respectively. The foci may 
be determined as follows : With B as a center and a radius 




Fig. 40. — Construction of ellipse, first method. 

equal to CAj (one-half the major axis) describes arcs cutting 
the major axis in the points F and F x which are the desired foci. 
The sum of the distances from any point on the ellipse to F and 
F T must equal the constant distance represented by the major 
axis AA a . The point B Tone end of the minor axis) is a point 
on the ellipse since by construction 

FB + F X B = 2A X C = AA X . 
Assume any point on AA, lying between F and F l5 such as P. 
With F as a center and a radius equal to A X P describe an arc. 



CONIC sections 45 

With F, as a center and a radius equal to AP, describe a second 
arc cutting the first arc in the points M and M x . These two 
points are on the ellipse since 

MF + MF T — AP -f AjP = AA X . 
In like manner other positions of P may be assumed and further 
points of the ellipse obtained. 

If it is clearly perceived that the sum of the distances from 
the foci to one extremity of the minor axis must be equal to the 
major axis (i. e., FB -j- F X B — AA X ) no difficulty should exist 
in plotting an ellipse from any of the following combinations of 
known data: (i) the major and minor axes, (2) the major axis 
and one or both foci, (3) the minor axis and one or both foci. 

At a given point on the ellipse to construct a tangent: Let R 
be the given point. Draw RF and RF., ; TR bisecting the angle 
thus formed is the required tangent. 

At a given point outside the ellipse to construct a tangsnt: 
Let X be the given point. With F x as a center and AA X as a 
radius describe an arc. With X as a center and XF as a radius 
describe a second arc cutting the first arc in the points H and K. 
Draw FjK and F X H cutting the ellipse in the points Z and Y 
which are points of tangency. The required tangents are XZ 
and XY. 

To Construct an Ellipse. Second Method. 

Given: The major and minor axes. In Fig. 41 let AA X and 
BB X be the major and minor axes respectively. With AA X and 
BB, as diameters describe two concentric circles and through 
the center draw any number of radial lines. At the points where 
the radial lines intersect the smaller circle draw horizontal lines. 
At the points where the radial lines intersect the larger circle 
draw vertical lines. The horizontal and vertical lines intersect 
at points of the required ellipse. 

To construct a tangent at any point on the ellipse such as R; 
draw a tangent to the outer circle at R r This tangent produced 
meets the major axis at T. The required tangent to the ellipse 
is T R. 



4 6 



MECHANICAL DRAWING 



37. The Parabola. — A parabola is generated by a point mov- 
ing in a plane so that its distance from a fixed point is constant- 
ly equal to its distance from a given straight line. The given 




Fig. 41. — Construction of ellipse, second method. 

point is the focus and the straight line is the directrix. The axis 
is a straight line drawn through the focus and perpendicular to 
the directrix. The vertex is the point of intersection between 
the curve and the axis, and lies midway between the focus and 
the directrix. 

To Construct a Parabola. First Method, Fig. 42. 

Given: The focus and directrix. In Fig. 42, F is the focus, 
DD X the directrix, AA t the axis, and V, midway between F 
and A, is the vertex. At any point on the axis, as P, erect the 
perpendicular MPM n . With F as a center and AP as a radius 
describe an arc cutting the perpendicular through P at the points 
M and M x which are two points on the required curve. The 
law governing the motion of the generating point is fulfilled 
since 

MF --= AP = DM 

Other points, such as N and N\ may be obtained in like manner. 



CONIC SECTIONS 



47 



At a given point on the parabola to construct a tangent: Let 

N be the given point. Draw NF and NC ; TN bisecting the 
angle thus formed is the required tangent. 
DJ234S678 9/\ 




Fig. 42. — Construction of parabola, 
first method. 



Fig. 43. — Construction of para- 
bola, second method. 



At a given point outside the hyperbola to construct a tangent: 

Let X be the given point. With X as a center and XF as a 
radius, describe an arc intersecting DD 1 at G and K. Through 
G and K draw lines parallel to the axis, AA X , intersecting the 
curve in the points of tangency H and L. The required tan- 
gents are XH and HL. 

To Construct a Parabola. Second Method, Fig. 43. 

Given: The abscissa VC and the double ordinate AB. 

Draw DA and EB equal and parallel to VC, and draw DE 
parallel to AB. Divide DA and AC into the same number of 
equal parts. From the divisions on DA draw lines to V and 
through the divisions on AC draw lines parallel to VC. The 
lines drawn from corresponding points of division intersect in 
points on the parabola. 

38. The Hyperbola. — An hyperbola is generated by a point 
moving in the same place so that the difference of its distances 
from two fixed points remains constant. 



4 8 



MECHANICAL DRAWING 



To construct an hyperbola: In Fig. 44 let Wj represent the 
constant difference, and let the two foci F and F x be the two 
fixed points so placed that FV = F^j. 




w 
*&-£* 



Fig. 44. — Construction of hyperbola. 

Draw BBj, the perpendicular bisector of VV^. With F as 
a center and any radius greater than FV X , as FP, describe an 
arc. With F x as a center and a radius equal to FP — Wj de- 
scribe a second arc cutting the first arc in the points N and N x . 
These points will lie on the hyperbola since 

FP = (FP— WJ = W x 
which satisfies the law governing the motion of the generating 
point. In a similar manner other points may be obtained. 

If F x is used as a center for the larger radii and F as a center 
for the smaller, the other branch of the hyperbola will be ob- 
tained. 

At a given point on the hyperbola to construct a tangent: Let 
R be the given point. Draw RF and RF t ; TR bisecting the 
angle thus formed is the required tangent. 



CONTC SECTIONS 49 

At a given point outside the hyperbola to construct a tangent: 

Let X be the given point. With F x as a center and VV\ as a 
radius describe an arc. With X as a center and XF as a radius 
describe the arc FGK cutting the first arc in the points G and 
K. Draw FK and F X G cutting the hyperbola in the points of 
tangency Y and Z. The required tangents are XY and XZ. 

If C, the point of intersection of the two axes be taken as the 
point through which the tangents to the hyperbola are to be 
drawn, the points of tangency will lie at infinity and the tangent 
lines will be asymptotes. 



CHAPTER V. 



Orthographic Projection. 

39. Orthographic Projection is the art of representing an ob- 
ject on one or more planes so as to graphically show the lengths 
and shapes of its lines and surfaces. All working drawings in- 
tended to convey exact technical information from the designer 
to the reader are made in accordance with the principles of or- 
thographic projection. Technical drawing is a graphic language 
of universal usage, its alphabet and vocabulary being the char- 
acter of lines, conventions, and symbols previously discussed, 
and orthographic projection its grammar. 

40. Projection on One Plane. — An object is projected onto any 
desired plane by drawing through the various points of the ob- 




Fig. 45. — Projection of an object onto a single plane of projection. 

ject lines perpendicular to the given plane; the points in which 
these lines pierce the plane are the projections of the correspond- 
ing points of the object. The projecting lines are called projec- 
tors and the plane onto which the object is projected is the plane 
of projection. Thus in Fig. 45 the object has been projected onto 



ORTHOGRAPHIC PROJECTION 



51 



tht plane as shown. The resultant projection represents the ob- 
ject as it would appear if viewed from in front, the point of sight 
being an infinite distance away. This view alone describes only 
the front face of the object and gives no information as to the 




Fig. 46. — Cast iron fork projected onto three planes of projection. 

shape of the top and sides. In order, therefore, to completely 
represent any object it must, in general, be projected onto three 
different planes, thus showing three views. The planes are gen- 
erally placed so as to be mutually perpendicular (as the top, 



52 MECHANICAL DRAWING 

front and side of a box), the resultant projections showing the 
object as though viewed successively from the top, front and 
side. 

41. Projection on Three Planes. — In Fig. 46 is shown a cast iron 
fork surrounded by three planes which may be regarded as trans- 
parent. The top plane lettered H is called the horizontal plane 
of projection, the plane in front lettered V is called the vertical 
plane of projection, and the plane at the side lettered P is called 
the profile plane of projection. By letting fall from the object 
lines perpendicular respectively to each of these planes, three 
views of the fork are obtained. The projection on the H plane 
represents the fork as it would appear were the observer look- 
ing down upon it; the projection on V represents the fork as 
though viewed from in front; and the projection on P represents 
the fork as though viewed from the side. These three views 
graphically describe all lines and surfaces of the fork, and 
taken in conjunction give the three dimensions, length, breadth 
and thickness. 

The line of intersection between the H and V planes is known 
as the ground line and is lettered GL. The line of intersection 
between the P and V planes is lettered XY. 

It is obviously impossible for the draftsman to actually draw 
on three mutually perpendicular planes. He is limited to the one 
plane as represented by his drawing paper. Some method, then, 
must be used for bringing the three planes containing the three 
views into one plane. This is accomplished as shown in Fig. 47 
by raising the H plane about GL as an axis until it is coincident 
with V, and revolving the P plane to the right about LY as an 
axis until it also is coincident with V. The three views are now 
found on one plane, the top view above the front view and the 
side view at the right of the front view. In practice the drafts- 
man, though employing mentally the process here given, does not 
draw the three planes but shows only the three views as given 
in Fig. 48. In Fig. 48 it should be noted that LX and LX 12 are 
revolved positions of the same line, LX 3 . 




Fig. 47. — The three planes of projection opened to form one plane. 



"l — r 
1 1 
j i_ 






> — 



\ 1 '■ ' ■ ' 



o o : 



— 1 — 1 — 1 — 1 — 

"A O V-- 



Fig. 48. — Top, front and side views of a cast iron fork. 



54 MECHANICAL DRAWING 

A dotted line is used to signify the invisibility of the line rep- 
resented. A line may be invisible in one view and visible in an- 
other. 

42. Fundamental Principles. — From the foregoing discussion 
and figures the following important principles are evident : 

i. If a line is perpendicular to a plane its projection on that 
plane is a point. 

2. If a line is parallel to a plane its projection on that plane 
will be parallel to the line. 

3. If a surface is perpendicular to a plane its projection on 
that plane is a line. 

4. If a surface is parallel to a plane its projection on that 
plane will show the true size and shape of the surface. 

5. The top and front views of any point lie in the same verti- 
cal line. 

6. The front and side views of any point lie in the same hori- 
zontal line. 

7. The side view of any point is as far from XY as is the 
top view from GL. 

43. Sequence of Views. — In general it is advisable to first con- 
struct that view most of whose lines are shown in true length. 
Let it be desired to show three views of the square based wedge 
illustrated in Fig. 49. It is evident that all lines of the base as 
well as the edge AB are parallel to H and hence the top view 
will be first constructed. At any convenient distance above GL 
draw a square, equal in size to the base of the wedge, and in the 
center draw a line equal to the length of the edge AB. The top 
view is now completed by connecting the ends of the edge with 
the corners of the square. 

The front view is a triangle whose base is equal in length to 
a side of the square, and whose altitude is equal to the height 
of the wedge. All points of the front view must lie vertically 



ORTHOGRAPHIC PROJECTION 



55 



under the corresponding points of the top view (Art. 42. Rule 

5)- 

To obtain the side view draw XY at any convenient distance 
to the rig-lit of the front view. Draw horizontal lines from the 




Fig. 49. — Three views of a wedge, pictorially showing method of 
obtaining side view. 

top view to XY, revolve to the right to meet GL, and let fall 
perpendicular lines. These perpendiculars intersect horizontal 
lines drawn from corresponding points of the front view in the 
desired points of the side view. 



56 



MECHANICAL DRAWING 



The student should never lose sight of the fact that the top, 
front and side views have been made on mutually perpendicular 
planes, and from these three views a mental conception of the 
entire object is gained. 

As an aid in properly locating the various points of an object, 
the points of the top view are lettered a, b, c. etc., the corre- 
sponding points of the front view a', b', c', etc., and the corre- 
sponding points of the side view a 1 ', b p , c p , etc. In actual draft- 
ing practice the points of a drawing are not lettered nor are the 
projecting lines shown. Also the center lines of the various 
views are made to serve the purpose of the ground line (GL) 
and the profile plane trace (XY). Until, however, the student 
has thoroughly mastered the principles of orthographic projec- 
tion, he will find it greatly to his advantage to letter all critical 
points, draw all projecting lines, and to draw and letter GL 
and XY. 

A few illustrative problems will now be considered. 

44. To Obtain the Top, Front and Right Side View of a Hollow 
Cylinder. Fig. 50. 




Fig. 50. — Hollow cylinder axis Fig. 51. — Hollow cylinder axis 

perpendicular to H. perpendicular to P. 

Given: The altitude and the outer and inner diameters of the 
cylinder; the axis of the cylinder to be perpendicular to H. 



ORTHOGRAPHIC PROJECTION 57 

The top view consists of two concentric circles of the given di- 
ameters. 

For the front view construct a rectangle whose width is equal 
to the diameter of the larger circle and the altitude equal to the 
given altitude. Within this rectangle construct a second rectan- 
gle of equal altitude but whose width is equal to the diameter of 
the smaller circle. The limiting lines of the inner rectangle are 
invisible and hence are dotted. 

The right side view is identical with the front view ; or it may 
be obtained by projecting the points of the top view onto XY, 
revolving to meet GL, and letting fall perpendiculars to meet 
horizontal lines drawn through the corresponding points of the 
front view. 

45. To Obtain the Usual Three Views of a Hollow Cylinder. 
Fig. 51. 

Given: As in the preceding problem except that the axis is 
perpendicular to P. 

Since the axis of the cylinder is perpendicular to P the center 
lines of the rectangles forming the top and front views are paral- 
lel to GL. 

The construction of the three views is obvious. 

46. To Obtain the Usual Three Views of a Cone. Fig. 52. 
Given: The diameter of the base and the altitude; the axis 

to be perpendicular to H; the apex pointing towards H. 

The top view consists of a circle whose diameter is equal to 
the given diameter of the base. 

The front view is an isosceles triangle whose base is equal to 
the given diameter and the altitude equal to the given altitude of 
the cone. 

The side view is identical with the front view, or it may be 
constructed by the indicated revolution. 

47. To Obtain the Top, Front and Left Side Views of the Frus- 
trum of a Cone. Fig. 53. 

Given: The altitude and the diameters of each of the bases; 
the axis perpendicular to P ; the larger base nearer the profile 
plane. 
5 



58 



MECHANICAL, DRAWING 



The top and front views are identical, each one consisting of 
a trapezoid of the given altitude, the two ends being equal in 
length to the given diameters of the bases. 




Fig. 52. — Cone axis perpen- Fig. 53.— Frustrumof a cone, axis 

dicular to H. perpendicular to P. 

The left side view may be obtained by placing the profile plane 
at the left and revolving the points of the top view counter- 
clockwise as shown. The result of this revolution is two concen- 
tric circles with diameters equal to the given diameters of the 
bases. The smaller base is not visible from the left and hence 
the inner circle is dotted. 

48. To Obtain the Top, Front and Eight Side Views of a Hexago- 
nal Prism. Fig. 54. 

Given: The altitude, and the size of the base; the axis to be 
perpendicular to H ; two faces parallel to V. 

The top view consists of a regular polygon of given size, two 
sides being parallel to GL. 

The construction of the front and side views is obvious. Note 
that in the front view the edges m'n' and kT are invisible but 
coincide with the visible edges c'd and e'f respectively. A 
similar case occurs in the side view. 

In Fig. 55 is shown three views of the same hexagon except 
that two faces are now perpendicular to V. 



ORTHOGRAPHIC PROJECTION 



59 




Fig. 54. — Hexagonal prism two 
faces parallel to V. 



Fig- 55-— Hexagonal prism two 
faces perpendicular to V. 



49. To Obtain the Usual Three Views of a Hexagonal Prism. 
Fig. 56. 

Given: The altitude, and the size of the base; the axis to be 
perpendicular to P ; no face to be either parallel or perpendicular 
to H or V. 

It is evidently more convenient to first construct the side view. 



L 


g . 




n 


k 


-— <- 
— ■ i- 


"''•~^ 


1 
f 


e 
m 


'""-^ X 

V, \ \ 


d 
b 


c 

a 


X '■ \ '"■ 


! 1 




v» > ', ' . 1 1 


ri 


rri 




_4-kk4iief 


t 


fc 

a' 


--*- 


1 

8 
I! 
d 


\ A ! d\|P 


i 

c' 




--4- 


c^d/ j/ 


f 




e 


"" 


t 



Fig. 56. — Hexagonal prism axis perpendicular to P. 
To construct the side view; at any convenient distance be- 



60 MECHANICAL DRAWING 

tween GL and to the right of XY draw a regular hexagon no 
side of which is either parallel or perpendicular to GL or XY. 

To construct the top view; project the points of the side view 
to GL, revolve counter-clockwise to XY, and draw ab, cd, 
etc., equal in length to the given altitude. The lateral edges 
CD and EF are invisible when viewed from above H (that is, 
when looking down on the side view from above GL), hence 
cd and ef are dotted. The top view is completed by drawing 
ga and gb. 

To construct the front view; project the points of the top 
view downward to meet horizontal lines drawn from the cor- 
responding points of the side view. The lateral degrees GH and 
KL are invisible when viewed from in front of V (that is, when 
looking at the side view from the left of XY), hence g'h' and 
kT are dotted. 

50. Revolution. — In the foregoing illustrations the objects 
were situated in the simplest position relative to the planes of 
projection, that is, with as many lines as possible parallel to H, 
V and P. This is the natural way of placing an object and 
would be the one chosen were the choice left to the convenience 
of the draftsman. It is sometimes necessary, however, to rep- 
resent an object with axis oblique to one or more of the planes 
of projection. 

Conceive three lines passed through the object and intersect- 
ing at its center, one of the lines being perpendicular to H, the 
second perpendicular to V, and the third perpendicular to P. 
The object may be brought into obliquity with any desired plane 
of projection by revolving the object about the proper one of the 
foregoing three lines as follows : 

First, the object may be revolved about the line perpendicular 
to H, which has the effect of turning it on its base to the right or 
left. 

Second, it may be revolved about the line perpendicular to V, 
causing the object to lean to the right or left. 

Third, it may be revolved about the line perpendicular to P, 
causing the object to tip forward or backward. 



ORTHOGRAPHIC PROTECTION 



6l 



If an object be represented in its simplest position and is then 
revolved in any one of the foregoing ways, two views will be 
changed while the third view will remain identical with the cor- 
responding view of the object in its original position. The un- 
changed view will lie on that plane of projection to which the axis 
of revolution is perpendicular and should be the first view con- 
structed. 

In Fig. 57 are shown three views of a wedge in its simplest po- 
sition . The arrow points are placed on the projecting lines to in- 
dicate the direction in which they were drawn. 

In Fig. 58 the wedge has been revolved from its original posi- 
tion through an angle of 45 ° to the right about an axis perpen- 

X 




Y 

Fig. 57- Fig- 58. 

Wedge revolved about an axis perpendicular to H. 

dicular to H. The top view is identical with the top view of Fig. 
57, except that the sides make an angle 45 ° with GL. During 
this revolution all points of the wedge remain the same distance 
from H. Hence the front view of Fig. 58 is constructed by let- 
ting fall perpendicular lines from points of the top view to meet 
horizontal lines drawn from corresponding points of the front 
view of Fig. 57. The side view is constructed in the usual 
manner. 

In Fig. 60 the wedge has been revolved .from its original posi- 
tion through an angle of 45 to the right about an axis perpen- 



62 



MECHANICAL DRAWING 



dicular to V. The front view is identical with the front view of 
Fig. 59 except that it leans to the right at an angle of 45 °. Dur- 
ing this revolution all points of the wedge remain the same dis- 




Fig. 59. Fig. 60. 

Wedge revolved about an axis perpendicular to V. 

tance from V. Hence the top view is constructed by erecting 
perpendicular lines, from the points of the front view, to meet 
horizontal lines drawn from corresponding points of the top 
view of Fig. 59. The side view is constructed in the usual 
manner. 

In Fig. 62 the wedge has been revolved from its original posi- 
tion backward through an angle of 30 about an axis perpendicu- 
lar to P. The side view is identical with the side view of Fig. 
61 except that it tips backward. During this revolution all points 
of the wedge remain at the same distance from P. Hence the 
top view is constructed as follows : From points on the side 
view erect perpendiculars to GL, revolve to XY, and draw hori- 
zontal lines to meet vertical lines let fall from corresponding 
points on the top view of Fig. 61. The front view is obtained by 
drawing horizontal lines from points on the side view to meet 
vertical lines let fall from corresponding points of the top view. 

Careful attention is needed to ascertain those lines which are 
invisible and hence dotted. 

51. Successive Revolutions. — In the problems of Art. 50 the 
initial position of the wedge was the same before each revolu- 



ORTHOGRAPHIC PROJECTION 



63 



tion. It is sometimes necessary for the draftsman to revolve an 
object about a certain axis, and from that position to again re- 
volve it about a second axis, and possibly to again revolve it 
about a third axis. In this manner the object can be placed in 
any conceivable position relative to the planes of projection. No 





d 


^"-^S^-^ 




b 






^^^ 


^"-^-^ 


c 




Fig. 6r. 




Fig. 62. 
Wedge revolved about an axis perpendicular to P. 

principles are used in successive revolutions other than those de- 
veloped in the preceding articles. 

In Fig. 63 is shown the original position of a pyramid and its 
successive revolutions about axes perpendicular to H, V and P 
respectively. In revolving about the axis perpendicular to V 



6 4 



MECHANICAL DRAWING 




13 






ORTHOGRAPHIC PROJECTION 



65 



the front view is identical with the front view immediately pre- 
ceding, the other two views being constructed in the usual man- 
ner. 




Fig. 64. — Circle revolved successively about axes perpendicular to V and//. 

In revolving about the axis perpendicular to P the side view 
is identical with the side view immediately preceding. The 
auxiliary line G x Lj is used as an aid in reproducing this view. 




Fig. 65. — Cone revolved successively about axes perpendicular to Kand H. 

In Fig. 64 the original position of the circle is parallel to H 
and perpendicular to V, the top and front views only being 



66 



MECHANTCAI, DRAWING 




Fig. 67. 
Auxiliary plane of projection. 



ORTHOGRAPHIC PROJECTION 



67 



shown. The circle is then revolved about an axis perpendicular 
to V. The front view remains a straight line but is inclined to 
GL, at any desired angle. The top view is constructed in the 
usual manner. The circle is now further revolved about an axis 
perpendicular to H. The top view is identical with the preced- 
ing top view except that the axis makes any desired angle with 
GL. The front view is constructed as usual. 

In Fig. 65 is shown a cone which has been successively revolved 
about an axis perpendicular to V and about an axis perpendicu- 
lar to H. The original position of the cone was taken so as to 
make the base parallel to H, the apex pointing downward from 
H. 

52. Oblique Plane of Projection. — An object is sometimes en- 
countered which can not be placed so that all of its faces are 
parallel to the three planes of projection. One face, at least, 
may be oblique and this face may be best shown by projecting it 
onto an auxiliary parallel plane. The projection on this paral- 
lel plane will show the true shape and size of the face. A case 
of this kind is illustrated in Fig. 66, the orthographic projection 
being shown in Fig. 67. 

It is frequently sufficient to project only the oblique face onto 




Top V/ew 



L eft Side View 



Fig. 68. — Auxiliary end view of pipe elbow, 
the auxiliary plane and to disregard, in that view, all other lines 
of the object. Thus in Fig. 68 only the oblique flange is projected 



6S 



MECHANICAL DRAWING 



onto the parallel plane whose line of intersection with H is AB. 
The auxiliary plane is then revolved about AB as an axis until 
coincident with H. 

53. Sectional Views. — The internal construction can sometimes 
be shown to best advantage, by passing an imaginary cutting 
plane through the object and theoretically removing that part 
of the object which lies between the observer and the cutting 
plane. In Fig. 69 is shown a top view and a vertical section of 




Fig. 69. — Top view and cross section of a cylinder cover. 

a cast iron cylinder and cover. Note that the cutting plane passes 
through two bolts but that these bolts are not cross hatched. It 
is an idiom of the graphic language that bolts, arms of pulleys, 
webs, keys, shafts, and gear teeth are never cross hatched. More- 
over in Fig. 55 only two bolts are shown in section, whereas it is 
obvious that five could be seen in the sectional view. The loca- 
tion of these bolts, however, is clearly shown in the plan and 
their position in the sectional view would appear peculiar and 
confusing. Practical utility warrants the statement that the 



ORTHOGRAPHIC PROJECTION 



6 9 



sectional view should show only that data which conveys useful 
information and discard all else even though pure theory would 
require it to be shown. 

The cross section of a pulley is shown in Fig. 70. The arm is 



Section on AB 




Section onAB 




Not thus § 77? us 

Fig. 70. — Front view and cross sections of a pulley. 

not cross hatched but the shape is shown by a separate section 
revolved into the plane of the paper. 

The draftsman may legitimately make use of the fact that an 




Fig. 71. — Top view and half section of a Hill coupling, 
object is symmetrical about a certain axis, by showing one-half 



?o 



MECHANICAL DRAWING 



the view full and the other half in section. Fig. ji illustrates 
this practice. 

It is sometimes convenient to represent only a small part of a 
surface as removed in order to show in section the construction 




Fig. 72. — Globe valve showing broken section, 
lying beneath. Such a view is called a broken section and is il- 
lustrated in Fig. 72. 



ORTHOGRAPHIC PROJECTION JL 

PROBLEMS. 
Geometric Solids. 

Each of the following problems may be placed in a space 
5" x.5". The layout of a plate which is adaptable to spaces of 
this size is shown in the appendix. 

The expression "three views" is understood to mean the top, 
front and side views. 

ia, ib, ic. Draw three views of a hollow cylinder. Fig. 73, with 
(a) axis perpendicular to V; (b) axis perpendicular to H; (c) 
axis perpendicular to P. 

2a, 2b, 2c. Draw three views of a cone. Fig. j$, (a) axis per- 
pendicular to V, apex towards V; (b) axis perpendicular to H, 
apex away from H; (c) axis perpendicular to P, apex towards 
P. 

3a, 3b, 3c. Draw three views of a square based pyramid. Fig. 
73, (a) axis perpendicular to V, apex away from V; (b) axis 
perpendicular to H, apex towards H; (c) axis perpendicular to 
P, apex away from P. 

4a, 4b, 4c. Draw three views of a hexagonal pyramid, Fig. y^, 
(a) axis perpendicular to V, apex towards V; (b) axis perpen- 
dicular to H, apex away from H, no side of the base parallel or 
perpendicular to V; (c) axis perpendicular to P, apex towards 
P, two sides of the base perpendicular to V. 

5a, 5b, 5c. Draw three views of a triangular pyramid. Fig. y^, 
(a) axis perpendicular to V, apex away from V, no side of the 
base parallel to H; (b) axis perpendicular to H, apex towards 
H, one side of the base parallel to V; (c) axis perpendicular to 
P, apex towards P. 

6a, 6b, 6c. Draw three views of a hexagonal prism, Fig. y^>, 
(a), (b) and (c) as in problem 4. 

7a, 7b, 7c. Draw three views of a wedge. Fig. y^, ( a ) short 
edge nearest H, long side of base parallel to V; (b) base parallel 
to V, short edge farthest from V, short side of base parallel to H. 

8a, 8b, 8c. Draw three views of a triangular prism, Fig. y^, 
(a) axis perpendicular to V; (b) axis perpendicular to H; (c) 
axis perpendicular to P. 



72 



MECHANICAI, DRAWING 




Fig. 73. — Geometric objects. 



coa/£, rtrusr/euM. 



orthographic projection 73 

9. Draw three views of a flight of steps, Fig. 73. Scale 1" = 
i'-o". 

10a, 10b, ioc. Draw three views of a frustrum of a square 
based pyramid, Fig. y^, (a) axis perpendicular to V, small base 
nearest V; (b) axis perpendicular to H, large base nearest H; 
(c) axis perpendicular to P, large base nearest P. 

11a, 11b, lie. Draw three views of a cross, Fig. 73, (a) face 
marked "A" nearest V; (b) "A" nearest H; (c) "A" nearest P. 

12a, 12b, 12c. Draw three views of a frustrum of a cone, Fig. 
73, (a), (b) and (c) as in problem 10. 

Machine Details. 

13. Draw top and front views of a monkey wrench. Fig. 74. 
Scale 

14. Draw front view and longitudinal section of a bearing, 
Fig. 74. Scale 

15. Draw three views of a bracket, Fig. 74. Scale 

16. Draw three views of a support. Fig. 74. Scale. 

17. Draw an end view and longitudinal section of a flange 
connection, Fig. 75. Half size. 

18. Draw three views of a pivot. Fig. 75. Half size. 

19. Draw three views of a bearing, Fig. 75. Scale 3" = i'-o". 

20. Draw three views of a pedal. Fig. 75. Scale i^i" = i'-o". 

21. Draw the top, front, and auxiliary plane view of a lever, 
Fig. 76. Scale 3"= i'-o". (Break the rod in order to shorten 
length.) 

22. Draw three views of a rod support, Fig. 76. Scale 3" = 
i'-o". 

2^. Draw three views of a packing gland, Fig. 76. Half size. 

24. Draw three views of a lever support, Fig. 76. Full size. 

Kevolution. 

An entire plate had best be devoted to each of the following 
problems. If a plate of the size shown in the appendix is used, 
each group of three views will be placed in a rectangle 5" x 7^2". 

25. Draw three views of a wedge, Fig. 73, axis perpendicular 
to H, short edge nearest H, and long side of base parallel to V, 

6 



74 



MECHANICAL DRAWING 




Cast /ron 



Fig. 74.— Machine details. 



ORTHOGRAPHIC PROJECTION /5 

and revolve it (a) through an angle of 15 to the right about an 
axis perpendicular to H; (b) through an angle of 45 to the left 
about an axis perpendicular to V; (c) forward through an angle 
of 45 about an axis perpendicular to P. 

26. Draw three views of a hexagonal prism. Fig. 73, axis per- 
pendicular to H, two sides of the base parallel to V, and revolve it 
(a) 30 to the right about an axis perpendicular to V; (b) 30 to 
the right about an axis perpendicular to H; (c) 30 forward 
about an axis perpendicular to P. 

27. Draw three views of a hexagonal pyramid, Fig. y^, accord- 
ing to the instructions given in problem 26. 

28. Draw three views of the frustrum of a pyramid. Fig. y^, 
axis perpendicular to H, large base nearest H, two sides of base 
parallel to V, and revolve it (a) 30 to the left about an axis per- 
pendicular to H; (b) 1-5 ° to the left about an axis perpendicular 
to V; (c) 45 forward about an axis perpendicular to P. 

29. Draw three views of a triangular prism, Fig. 73, long side 
parallel to H and V, and revolve it (a) 30 to the right about an 
axis perpendicular to H; (b) 6o° to the left about an axis per- 
pendicular to V; (c) 45 backward about an axis perpendicular 
to P. 

30. Draw three views of a square pyramid, Fig. y^, axis per- 
pendicular to H, two sides of the base parallel to V, and revolve 
it (a) 15 to the right about an axis perpendicular to H; (b) 45 
to the left about an axis perpendicular to V; (c) 6o° forward 
about an axis perpendicular to P. 

Successive Revolution. 

31. Draw three views of a hollow cylinder. Fig. 73, axis per- 
pendicular to P, and revolve it (a) 30 to the right about an 
axis perpendicular to H; (b) from the position obtained in (a) 
revolve 45 ° to the left about an axis perpendicular to V; (c) 
from the position obtained in (b) revolve 30 backward about 
an axis perpendicular to P. 

32. Draw three views of a cone, Fig. 73, axis perpendicular 
to H, apex nearest H, and revolve it (a) 45 to the right about 
an axis perpendicular to V; (b) from (a) revolve 6o° to the left 



76 



MECHANICAL DRAWING 




Stee 



Fig. 75.— Machine details. 



ORTHOGRAPHIC PROJECTION 



77 



Forgecf Sfe e/ 




FACK/NG GLAND. 
Stee/ 



LEVER SUPPORT. 
$ fee/ 

Fig. 76. — Machine details. 



78 MECHANICAL DRAWING 

about an axis perpendicular to H; (c) from (b) revolve 30 
forward about an axis perpendicular to P. 

33. The same as problem 25 except that the revolutions are to 
be continuous. \ 

34. The same as problem 26 except that the revolutions are to 
be continuous. 

35. The same as problem 27 except that the revolutions are to 
be continuous. 

36. The same as problem 28 except that the revolutions are to 
be continuous. 

37. The same as problem 29 except that the revolutions are to 
be continuous. 

38. The same as problem 30 except that the revolutions are to 
be continuous. 

Auxiliary Views. 

39. Draw the top and front views of the given object in its 
simplest position. Obtain an auxiliary view projected onto a 
plane parallel to an inclined face. 

a. Wedge. 

b. Triangular prism. 

c. Square pyramid. 

d. Hexagonal pyramid. 

e. Frustrum of a square pyramid. 

The foregoing objects are dimensioned in Fig. 73. 



CHAPTER VI. 



Working Drawings. 

54. Clearness. — It has been previously stated that practically 
all working drawings are made in accordance with the principles 
of orthographic projection. The purpose of such a drawing is 
to give clearly all the information needed to construct the object 
represented. A drawing which does not fulfill this purpose is a 
failure, however artistic it may be in appearance and accurate 
in execution. Failure to clearly express the design is, in general, 
due to one of two main causes; either the information is not 
complete, due to an omitted view, dimension line, or note, or the 
information may be confused by an excess of data such as too 
many views, several separate notes pertaining to the same matter 
with possible confliction, needlessly repeated dimensions, or con- 
fusing lines due to a rigid adherence to the laws of projection. 
Lack of sufficient data is due partly to carelessness on the part 
of the draftsman and partly to his failure to theoretically place 
himself in the position of the one who is to use the drawing in 
order to ascertain if all needed information has been given. 
Excess of data, the second cause for failure in clear expression, 
is due partly to the mistaken belief that no idioms exist in 
graphic language, and partly to an inherent verbosity of ex- 
pression whether the language be English or graphic. To a 
great extent this matter is solely one of common sense and the 
following rules are offered merely as a general guide : 

i. Show only as many views as are necessary to completely 
portray the object. 

2. Do not repeat dimensions on one view which are clearly 
shown on another. 

3. Do not treat the same subject matter in several scattered 
notes. 

4. Written notes, figured dimensions, and the graphic line work 
must all be so clearly expressed as to render vagueness or 
ambiguity impossible. 

5. If, in any particular case, a law of projection conflicts with 



80 MECHANICAL DRAWING 

clearness, sacrifice the letter of the law and stick to clearness 
which is, in reality, the spirit of all laws of projection. 

The draftsman who is thoroughly aware of the fact that the 
fundamental test of any drawing is its readableness cannot go 
far astray. 

The rules just suggested, as well as other means to secure 
simple and clear expression, will be discussed in subsequent 
articles of this chapter. 

55. Assembly and Detail Drawings. — Working drawings are 
divided into two main divisions, assembly drawings and detail 
drawings. 

The purpose of the detail drawing is to portray each part of 
the machine or structure separately. The details may all be 
placed on one drawing with the name of the piece under each 
detail ; or, if there are many details, one drawing may consist 
solely of castings, another of forgings and still another of bolts 
and screws. Due to the probable great variance in size of the 
different pieces, it is frequently desirable to use several scales on 
the same detail drawing. In such a case the scale should be 
placed under each piece drawn. If all the pieces on one drawing 
are to be made from the same material, the name of the material 
is placed in the title. If various materials are represented on the 
same sheet, the material should be stated under each piece, and the 
title should read "Material as indicated." A "Bill of Material" 
is generally placed on each drawing, which is a tabulation of 
the name, material, and number required, of each piece. One 
column is usually left for remarks. Some firms prefer to omit 
the Bill of Material from the drawing and place it on a separate 
sheet which accompanies the drawing. 

An assembly drawing is a representation of the machine or 
structure as a whole with its various pieces in their proper places. 
On such a drawing is shown only the over-all dimensions and the 
distances from center to center of the various pieces in order 
that the drawing may be of service in erecting the machine or 
structure. 

If the object represented is sufficiently simple the assembly 
and detail drawings may be combined. In such a drawing each 



WORKING DRAWINGS Ol 

piece is completely represented and dimensioned and yet shown 
in its proper place in relation to the other pieces. 

56. The number of views required to completely represent an 
object will vary from two to possibly five or six. In general, the 
top, front and side views are required, though many simple 
objects may be clearly shown in two views. Frequently the top 
view and a cross section give an ample description, or the top 
view and front view. When only two views are shown the side 
view is seldom one of the two. A more complicated object may 
require the top, front, right and left side views, a view on an 
auxiliary plane, as well as several cross sections. The only guide 
in this matter is to remember that the machine or structure must 
be clearly and completely represented in as few views as possible. 

It has been previously shown that the logical arrangement of 
views requires that the front view be under the top view, and the 
side view at the left or right of the front view. This arrange- 
ment should be adhered to rigidly. In this connection it is of 
interest to note that the English practice is to regard the object 
as being above the horizontal plane and in front of the vertical 
plane. The planes are brought into coincidence by revolving the 
profile plane backward to coincide with the vertical plane, and 
lowering the horizontal plane until coincident with the verti- 
cal plan, the front view thus being shown above the top view 
and the side view at the right of the front view. This system 
has but little to recommend it and was discarded in the United 
States some twenty years ago. It is still used in England, though 
at various times attempts have been made to change to the system 
used in this country. 

57. Notes. — The language of graphics should be supplemented 
by the English language whenever additional clearness can be 
gained by so doing. Sometimes 'a well worded note will save the 
making of a view. The note should be lettered in lower case 
letters and should be so clearly expressed that a vague or ambigu- 
ous interpretation is impossible. 

58. Dimensioning. — The neat, accurate, and legible dimension- 
ing of a drawing is as important a part of the drawing as the 



82 MECHANICAL DRAWING 

actual graphic representation of the various views. In dimen- 
sioning a working drawing the draftsman must assume the point 
of view of the artisan who is to construct the object represented 
and give those dimensions which will best aid in the construction. 
The well equipped draftsman should have a working knowledge 
of the general methods used in pattern-making, casting, forging, 
and machine shop practice, in order that his designs may be con-; 
structed economically. 

The following rules for dimensioning represent the accepted 
practice of most modern drafting rooms : 

i. Dimension lines should be fine, continuous, black lines with 
an open space near the center for the insertion of the figures. 

2. Draw all dimension lines before inserting the figures. 

3. Figures should always read from the bottom or right side 
of the drawing. 

4. Arrow points should be neatly made and should touch the 
lines between which the dimension is given. 

5. Dimension only between center lines and finished surfaces. 

6. Do not give a dimension between dotted lines if it can be 
avoided. 

7. The total sum of a series of dimensions (called an "over-all" 
dimension) should always be given. 

8. Do not require the user of a drawing to add or subtract in 
order to obtain a desired distance. 

9. Do not repeat a dimension on one view which is clearly 
shown on another. Divide the dimensions between the various 
views by selecting the dimensions best suited to each view. 

10. Dimension lines should not be crowded close to other lines 
of the drawings, but should be placed clearly and conspicuously. 

11. In general place the dimension lines outside the view. 
Occasionally clearness may be gained by violating this rule. 

12. Do not place dimension figures on a center line or on a line 
of the drawing. 

13. Give diameters of circles and radii of arcs, and abbreviate 
diameter to Dia. or D. and radius to Rad. or R. 

14. Locate holes by giving dimensions to their center lines. 



WORKING DRAWINGS 



83 



15. Dimensions of less than two feet should be given in inches, 
as 17", 23", and two feet and over in feet and inches, as 2'-o", 
3'~7"- 

CORRECT D/ME/VStON/NG. 




/vor mus. 
/A/CORRECT 0/MENSION/NG. 




I 1 1 1 

II 1 
II II 




*— 
7J. 


■ 1 1 1 
11 . 1 1 


— ? 






—r- 




r~^s 




-f* 









I 






*-■*£• 

5 



> 



/£./%./£■ / &>&-'& 



/6 > 'S2 
THUS, 



A/or mi/<s. 



Fig. 77- —Correct and incorrect dimensioning. 
An exception to this rule is almost universally made in the case 
of shafts, pulleys, gears, wheels, wheel-base, cylinders, and pipes. 



84 MECHANICAL DRAWING 

this class of work being dimensioned in inches only, as 121" 
wheel-base, 48" pipe, 60" pulley, etc. 

16. The dividing line of a fraction should be made horizontal. 

17. The figures should read parallel to the length of a dimen- 
sion line and not perpendicular to it. 

18. If a dimension does not agree with the scaled distance, due 
to a change after the drawing has been made, underline the 
dimension figures or prefix the work "make." In this manner 
the draftsman indicates his knowledge of the discrepancy. 

19. Never cross hatch over a dimension figure. 

20. The cutting plane of a section should be shown by a dot 
and dash line and lettered. At each end of the line show by 
arrows from which side of the cutting plane the section is viewed. 
Mark the sectional view thus: Section on AB. 

21. To indicate that a surface is to be machined or "finished" 
an f is placed on that view of the surface which shows as a line. 
If all surfaces of the object are to be finished letter under the 
piece "finish all over" or the abbreviation "f. a. o." This latter 
statement is made in the title if applicable to all pieces represented 
on the drawing. Otherwise the title should read "Finish as 
indicated." 

In Fig. yy many of the foregoing rules are illustrated as well 
as some additional forms of dimensioning. This figure should 
be carefully studied. The primary cause for stating a dimension 
in one form rather than in another is increased clearness. 

59. Title. — The title is placed in the lower right hand corner 
of the sheet. The amount of space devoted to the title and the 
size of the letters depends upon the size of the drawing. For 
drawings 12" x 18", 18" x 24" and 24" x 36", the rectangular space 
reserved for the title may be 3^" x 2>4", aYa" x 3" and 5" x 3^" 
respectively. The lettering of the title should be free hand, ver- 
tical preferred, and of such a size as will artistically fill the space 
reserved. Nearly every engineering firm has its own standard 
title containing such information as is most suitable for the 
requirements of that particular firm. Many firms print the 
standard form for the title onto the tracing cloth, others use a 



WORKING DRAWINGS 



85 



rubber stamp, while still others leave the construction of the title 
entirely to the draftsman. Various titles have been designed for 
various needs so that it is impossible to give a form sufficiently 
general to cover all requirements. The following data is, how- 
ever, included on most title forms : 
1. Name of the firm. 

Name of machine or structure. 

Scale. 

Drawn by , traced by , checked by • 



2. 

3- 

4- 

5- 
6. 



Approved by 



Date; usually that of completing tracing. 

7. Number; for filing purposes. 

In small detail drawings the material and finish are sometimes 
included in the title. A characteristic free hand title is illus- 
trated in Fig. 74. 

60. Checking. — Before leaving the drafting room, a drawing 
should be carefully examined by someone other than the drafts- 



UN /TED T/i/?£AP CO. 

EA/G/NEEff/NG DEPARTMENT 

WALL BftAC/ffr. 



Material, Gatst/ron. 
Prawn by, £-.l.t. 
7raced Jby, S.i'/f 
Sc&/e-/~/ L 



Unfinished 

Checked by, d&E. 
Approved 6y. 7&&. 
/872. Ocr.Ji.i9/ J 



Fig. 78.— Typical title. 

man who executed it. In large drafting rooms "checkers" are 
employed whose sole duty is the examination of drawings. In 
smaller drafting rooms the draftsmen check each others work. 
The checker, by signing his name to the drawing becomes respon- 
sible for the accuracy and correctness of the work. The fact 



86 MECHANICAL DRAWING 

that a drawing is to be examined by a professional checker does 
not relieve the draftsman from the necessity of carefully and 
thoroughly examining his own work before turning it over to 
the checker. A drawing should be examined systematically 
according to some standard outline such as the one here sug- 
gested : 

1. Before checking any details read the drawing as a whole to 
see if the general meaning is clear. 

2. See if a sufficient number of views are given to clearly rep- 
resent each piece, and that there are no unnecessary or confus- 
ing views. 

3. See that the material, finish, and scale for each piece are 
properly stated. 

5. Carefully examine all dimensions to ascertain, that all neces- 
sary dimensions are clearly shown; that there are no superfluous 
ones ; that scaled distances agree with the given dimensions ; that 
no arrow points are omitted ; and that all dimensions are placed 
to the best advantage. 

6. Check all computations, and see that there is a sufficient 
amount of clearance wherever clearance is required. 

7. See that, wherever possible, standard sizes of bolts, screws, 
pipes, shafting, etc., have been specified. 

8. See that notes are briefly and clearly expressed. 

The student before handing in a plate should apply the fore- 
going examination and in addition should farther check his work 
to see, ( r ) that wherever an erasure has been made all lines 
affected have been re-inked; (2) that all visible lines are full and 
all invisible lines are dotted; and (3) that his name, date, number, 
and plate number are on the drawing. When the student finally 
hands in his plate at the office it is the equivalent of saying in 
words, "This plate has been executed with all the care and con- 
scientious work of which I am capable. It is a true measure of 
my present ability as a draftsman." 

61. Sketching. — The ability to rapidly execute a neat, readable 
sketch is essential to the engineer or draftsman. Those men 
whose time is valuable frequently express the general idea of a 



WORKING DRAWINGS 87 

design by means of a free hand sketch, leaving the execution of 
the working drawing to a draftsman. A good engineer can 
express his ideas as fluently, and even more clearly, by sketching 
than by talking. The draftsman is frequently required to make 
sketches of existing machinery which may be at some distance 
from the drafting room, and from these sketches to make the 
working drawings. It is this phase of sketching which will be 
discussed in this article. 

In sketching from an object these tools are necessary; paper 
(preferably cross section paper), a 3H pencil, a two-foot folding 
rule, and a pair of calipers. The sketch should be made entirely 
free hand, but its neatness and accuracy are limited only by the 
ability of the draftsman. The making of a sketch should be 
divided into three distinct parts as indicated by the following 
paragraphs. 

Views. — First decide on those views which will best illustrate 
the object. Sketch the views decided upon, judging relative 
lengths solely by the eye but as accurately as ability permits. 
Remember that too many views are better than not enough, since 
on the ultimate working drawing unnecessary data can easily be 
discarded. 

Dimension Lines. — After having made the requisite views place 
dimension lines on the sketch but do not fill in the dimension 
figures. A more systematic and thorough dimensioning of the 
sketch is insured in this way, than by diverting the attention to 
actually measure distances and fill in the figures. The danger at 
this point of the work is that not a sufficient number of dimension 
lines will be used. Regard the various views critically and see 
that a dimension line is placed wherever it will be needed in the 
making of the final drawing. Draw all center lines and extension 
lines while placing the dimension lines. It will be noted that up 
to this point of the work handling of the object, which is apt to 
be greasy, oily, or dusty, is unnecessary, thus insuring a neater, 
cleaner, sketch than would be the case were the object handled 
frequently and needlessly. 

Dimension Figures. — -By means of the two-foot rule and cali- 



88 MECHANICAL DRAWING 

pers obtain the dimensions from the object and record them in 
the proper dimension lines previously placed. 

It should be remembered that the sketching may be done at 
some distance from the drafting room, and that omitted data will 
cause trips to and from the drafting which should be regarded 
as an ignominious loss of time. Therefore the completed sketch 
should be subjected to a rigid examination, checking its various 
views and dimensions along the lines explained for working 
drawings in article 60. A well executed sketch should be sus- 
ceptible of translation into a complete working drawing by a 
draftsman other than the sketcher. 

62. Shade Lines. — The shade line is a heavy weight line used to 
indicate which surfaces are raised and which are depressed. 
Shade lines undoubtedly lend a touch of realism to the flatness of 
orthographic projection, and their use is to be commended when- 
ever the gain in clearness is sufficient to compensate for the addi- 
tional time required in execution. Some drafting rooms prohibit 
absolutely the use of shade lines, while a smaller number require 
shade lines to be used on all drawings. Neither of these extreme 
systems is to be recommended. It is not a matter to be settled 
by a fixed and unalterable rule, but should be given a more 
flexible treatment. The two adverse factors, gain in clearness 
and loss of time, must be balanced one against the other in guid- 
ing the judgment as to a wise use of shade lines. 

The light is regarded as coming from the upper left corner 
of the drawing in parallel rays, making an angle of 45 ° with the 
horizontal. A shade line is used to separate a surface which 
receives the light from one which does not. By sliding the 45 ° 
triangle along the T square and regarding the hypotenuse as a 
light ray, the surfaces receiving the light may be easily distin- 
guished from those which do not. In general, the lower and 
right hand edges of all raised surfaces should be shade lines, 
while on depressed surfaces the shade lines are placed on the 
upper and left edges. The line of intersection between visible 
surfaces is not shaded, nor should dotted lines be shaded. A 
circle representing a hole is shaded as follows: Draw a 45 ° line 
through the center extending upward to the left. Set the com- 



WORKING DRAWINGS 



89 



passes to the radius of the circle and place the needle point on 
the line just drawn and at a distance from the center of the circle 
equal to the desired maximum thickness of the shade line. 
Describe a semicircle which becomes tangent to the original circle 
on each side. A circle representing a raised surface is shaded in 
a similar manner except that the center for the semicircle is taken 
downward to the right. 

Fig. 79 is an illustration of the use of shade lines. 



n 
n 


(O) 


n 



Fig. 79- — Shade lines. 

63. Line Shading. — On display drawings or drawings intended 
for non-technical readers, it is highly desirable to represent more 
artistically and naturally the nature and relation of surfaces than 
is possible by the mere outline even though reinforced by shade 
lines. To gain a realistic effect surfaces in shade are distin- 
guished from those in light by line shading. In general a sur- 
face is shaded by a series of parallel lines which decrease in 
weight as the lighter portion of the surface is approached. The 
gradual increase in width of the spaces between the line further 
increases the effect of the surface becoming lighter. Concave and 
convex surfaces are readily shown in this way. 
7 



90 



MECHANICAL DRAWING 



The direction of the light is regarded to be such that the pro- 
jections of the light rays make an angle of 45 ° with the horizon- 
tal. In Fig. 80 is shown the top and front views of a cylinder. 
If a plane of light rays be passed tangent to the cylinder the line 
of tangency is the darkest element. The brightest element will 
be the one from which the light is reflected directly to the eye of 
the observer. Since the angle of reflection of a light ray must 
equal the angle of incidence it becomes obvious by an inspection 
of Fig. 80 that the brightest element is found 22^° to the left 
of the center line. 



\ I 




Fig. 80.— Position of light and dark elements of a cylindrical surface. 

The cast iron pipe shown in Fig. 81 is shaded according to the 
method just discussed. Note that, beginning at the lowest side 
of the convex portion, the lines grow gradually heavier and closer 
together until the darkest element is reached, and then become 
gradually lighter in weight and further apart until the lightest 
element is attained. From the lightest element to the top of the 
cylinder the lines maintain the same weight but the width of 
spacing gradually decreases. In the concave portion of the pipe 



WORKING DRAWINGS 



91 




Fig. 81. — Line shading. 



92 



MECHANICAL DRAWING 



the lightest element is below the center line and the darkest 
element above. The methods used in shading the other objects 
of Fig. 81 are obvious. It is perhaps worth while to observe 
that, due to the closeness of the lines, it is almost impossible for 
the engraver to satisfactorily reproduce line shading. Hence the 
artistic effect which can be gained by line shading is not fairly 
represented in these illustrations. 

The shading should progress from the bounding lines of the 
object inward toward the center, as it is easier to gradually 
increase the spacing than to decrease it. Center lines are not 
drawn in this class of work. 

Line shading is required by the United States Government on 
all drawings submitted to the Patent Office. 

64. Structural Drawing. — That portion of graphic language 
pertaining to the representation of all forms of steel construction, 
such as bridges, the skeleton framework for large buildings, etc.. 
is called structural drawing. The steel used in the construction 
is rolled in various standard shapes and fastened together per- 



^ffH\ , 



A7V7 




Fig. 82. — Rolled steel shapes. 

manently with rivets. The purpose of this article is to point out 
certain idioms of expression used in structural drawing as well 
as to illustrate the principal shapes and forms of riveting used in 
steel construction. 

The six most important shapes made in rolled steel are the 
I-beam, Channel, Z-bar, Angle, Tee, and Plate as illustrated in 
Fig. 82. In addition to these may be mentioned bars of various 
cross sections such as round, flat, and oval. These shapes are 
rolled in numerous standard sizes and are catalogued in the hand- 
books of the various steel companies. 



WORKING DRAWINGS 



93 



The foregoing shapes are fastened together by rivets driven 
either by hand or machine, the latter being exclusively used 



•Shojo /? /VgAg 



P/a/n 



C?/7//Ofpea( 

Near r~ar £?ofh 
S/de S/'de. S/des 



./^/trrfened -£ '/?/c?h^ 



CounfersunK 
Near r~~ar &of/7 
S/de S/de. Sides 



,. /-y&fre/y&d. 



Near r^ar 



Side S/de 



o n 







nir 



{Wu^m^4M^MM 



C7 



<Shop /?\ v&fs 



Bot/7 
Sides 



.r~/& t fan ed §■"/?/ ah . 



/Year rar &of/? 
Side S/de. S/des 



/^/e/d r?/ve.fs 



C/7/ppe.o/ ^ 

A/&ar far £3qf/7 
S/W& S/de S/des 



10 O 



# * 



tit 



T>»v>m>&mm. 




Fig. 83. — Standard representation of rivets. 

wherever much riveting is to be done. All possible riveting is 
done at the shop, but a certain, remainder must be driven in the 
field. One duty of the structural draftsman is to indicate which 
rivets are to be driven in the shop and which in the field. It must 



94 MECHANICAL DRAWING 

also be shown whether the rivet heads are full, flattened, or 
countersunk. Fortunately there is a universally accepted stand- 
ard for the representation of rivet heads. The symbols shown 
in Fig. 83 are so commonly known as to require no explanation 
when used on a drawing. Rivets vary in diameter from ^" to 1". 

The method of showing a section in structural drawing differs 
from that to which the machine draftsman is accustomed. In 
Fig. 83 is shown an end section of the two angles and plate. 
Note that instead of cross hatching the cut material it is made 
solid black. The two angles are, of course, in actual contact with 
the plate, yet a hair line of white, or "streak of daylight" as it is 
sometimes called, is left between the pieces. This violates the 
letter of the law yet is justified by the increased clearness, for 
were the hair line of white omitted the section would become an 
unintelligible mass of black ink. 

Dimension figures are placed just above the dimension lines, 
and dimensions over one foot are given in feet and inches, thus 
differing from machine drawing in both particulars. 

The word "pitch" is used to indicate the distance from center 
to center of rivets which are equally spaced. Thus, if "3" pitch" 
be written just above a dimension line extending from one rivet 
to another, it is to be understood that all rivets included between 
the two extreme ones are 3" apart center to center. 

The size of an angle is stated thus, 5" x 3^" x 5 / 16 " angle, 
the first two dimensions being the over-all lengths of the legs 
and the third representing the thickness of the material. The 
longer length is stated first. 

In giving the size of a Z-bar, Channel, or I-beam, the over-all 
length of one leg, the distance back to back of the legs, the over- 
all length of the other leg, and the thickness of the material are 
stated in the order named, thus: 3^2" x 6" x 3^" x 3 / 16 " Z-bar, 
3/ 2 "xio"x3/ 2 "x/ 2 " Channel, or 4" x 3" x 4" x %" I-beam. 

The size of a Tee is stated thus, 4" x 4" x y 2 " Tee. 

The length, width and thickness of a plate is given thus, 
i2'-o"x8"x/ 2 " plate. 

A Bill of Material must always accompany a structural draw- 
ing, either on the drawing, or separately. 



CHAPTER VII. 



Bolts and Screw Threads. 

65. Since bolts and screws are the commonest forms of fasten- 
ings for machines, it behooves the draftsman to have a working 
knowledge of their formation. Fortunately the important dimen- 
sions are fixed by the United States Government and are regarded 
as standard. The purpose of this chapter is to indicate the con- 
ventional representation of bolt heads and nuts and screw threads. 

66. The Helix is generated by a point moving around a given 
straight line and at the same time in a direction parallel to the 



m' 





Fig. 84. — Construction of Helix, and application to square screw threads, 
straight line, the two motions being uniform. The curve of a 
screw thread is the helix. 



9 6 



MECHANICAL, DRAWING 



To construct a helix : In Fig. 84 let the circle adgj be the 
horizontal projection of the circular path of the generating point 
and let the line m'n' — mn be the given straight line. Divide 
the circle and the straight line into any number of equal parts, 
in this case twelve. Consider the initial position of the generating 
point to be at a. As the point moves from a to b on the circle it 
must ascend 1 / 12 of the length of the line m'n' ; similarly when 
the generating point has reached d on the circle it must have 
ascended y± of the length of m'n'. Therefore from a, b, c, etc., 
erect perpendicular lines to meet horizontal lines drawn from the 
corresponding points of division on m'n'. The corresponding 
vertical and horizontal lines meet in points on the desired helix. 
The pitch is the distance the generating point moves along the 
line while making one complete revolution around it. 

67. Various Forms of Screw Threads are in use which may be 
roughly divided into two classes, V threads and square threads. 
In general the V threads are used solely as fastenings and the 
square thread used to transmit power. In Fig. 85 are shown 





SHARP 1/ 

| c Pitch ,| 



SQUARE 




& U. S. STANDARD 

P/tah. 

21 




WH/TWORTH 

\,Pitch \ 




acme: AtL/rrRfss 

Fig. 85. — Standard screw threads, 
cross sections of various types of threads. The United States 
Standard thread is the one most commonly employed in this 
country, while the Whitworth thread is the English Standard. 

The standard proportions adopted in this country are as 
follows : 

Let P = pitch, D = outside diameter and N = number of 
threads per inch ; then 



P= =lf = 0.241 



D t 0.625 — O.175. 



BOLTS AND SCRFW THREADS 



97 



It will be observed, then, that the determination of either P, N 
or D immediately fixes the values of the other two. Thus, if the 
pitch desired is %", N must equal 8 and the value of D may be 
deduced from the formula or by reference to one of the common 
tables of screw thread proportions. 

A double screw thread consists of two threads, side by side, 
wound around the cylindrical core. 






SINGLE V 



S/NGLEV 



SINGLE V 






DOUBLE (/ DOUBLE V SINGLE SQ. DOUBLE SQ. 

Fig. 86. — Conventional representations of screw threads. 

Threads may be either right hand or left hand; the former 
advance away from the body when turned clockwise and the 
reverse is true for the latter. A left hand thread should be 
plainly marked on the drawing with the abbreviation L. H. 

68. Conventional Representation. — It would be an absurd waste 
of time to show all screw threads as helixes. In Fig. 86 are 
shown several conventions for the representation of threads. The 
most, frequently used conventions for single Y threads are those 
given at B and C. The spacing of the lines is clone solely by the 



9 8 



MECHANICAL DRAWING 



eye and the root lines are made heavier for effect. It is not 
necessary to actually draw the correct number of threads per 
inch. If the thread is standard mark it so and give the outside 
diameter. The threads shown in Fig. 86 are all right hand; left 
hand threads would slant in the opposite direction. 

Some of the threads in Fig. 86 are shown partly in section 
merely to illustrate the construction. Note that the inner threads 
are not parallel to the outside threads- — shown at A and D — but 
in the conventional representation shown at B and C all thread 
lines are made parallel for ease in drawing. 

Two tapped holes are shown in Fig. 87, one in section and the 
other in elevation. Note that both of these holes are to receive 




Fig. 87. — Tapped holes, in elevation and section. 

right hand threads, hence the thread lines in the sectional view 
must slant in the opposite direction. 

69. Bolt Heads and Nuts are generally square or hexagonal, 
and may be either chamfered or rounded. The chamfered nuts 
and heads are used on general work where nicety of finish is not 
desired, while the rounded forms are used on finished machinery 
where beauty as well as utility is a factor. 

Three dimensions, pertaining to heads and nuts, have been 
fixed by the Government as standard : ( 1 ) the short diameter 



r. 



^Across forne,rs\ 




T 
1 

/iex. nut and head. 
RouncS. 



Trial- 



Trial 




/iex nut anal 
hecrc/. Chamf. 





/=-- 



< r— *h 

Across Corners 




^i,JQ3 






Cha/rtf. 



X- 




lOO 



MECHANICAL DRAWING 



or distance across flats, (2) the thickness of the nut, (3) the 
thickness of the head. In Fig. 88 are shown various forms of 
hexagonal and square nuts and heads, whose construction is 
obvious from an examination of the figures. It is not necessary 
to draw a plan of a head or nut merely to ascertain the value of 
F, the distance across corners, since this distance can be obtained 
by the geometrical operation shown in both figures. It is, of 
course, evident that in elevation the two side faces of a hexagonal 
nut or head are each one-half as wide as the front face. 

A nut or head should generally be drawn across corners, thus 
showing graphically the amount of clearance needed. Some 
drafting rooms even make it a fixed rule to require all nuts and 
heads to be drawn across corners in all views. 

A standard nut or head is not dimensioned on a drawing but 
is marked "U. S. Standard" stating whether it is hexagonal or 
square and whether chamfered or rounded. 

A lock nut is shown in Fig. 89. This nut is used on quick mov- 



AOCK A/UT 



&TUD BOLT 




SETSCffE-WS 

O,, CD 



rin 







CONE 



w^O 



\\\^\\<^ 



ROUND\^^ l-psa SUNK 




Fig. 89. — Lock nut, stud bolt, and set screws. 



ing parts where a single nut could be easily loosened. Frequently 
both nuts are made equal in thickness, in which case the thick- 
ness of each is made equal to V^ D, all the other dimensions being 
standard. 



BOLTS AND SCREW THREADS 



IOI 



70. Set Screws. — The purpose of a set screw is to prevent the 
motion of one piece by pressing against another. In Fig. 89 are 
shown several forms of heads and ends. 



r=u=^ 



ROUND 



¥ 



¥ 



OVAL FLAT 

Fig. 90. — Machine screws. 



r/USTF/? 



The character of the ends is dependent upon the amount of 
resistance necessary. The resistance developed by the end of a 



f?AG BOLT 



££W/S &oir 




Fig. 91. — Foundation bolts, 
set screw which protrudes into another piece is of course greater 



102 MECHANICAL DRAWING 

than an end which depends upon friction alone, but with the 
disadvantage of requiring a cut in the piece touched. 

71. A Stud Bolt is a screw, one end of which is to receive a 
nut and the other end to fit a tapped hole. In Fig. 89, note that 
in order to avoid confusion the threads of the tapped hole are 
not shown. 

72. Machine Screws are used for fastenings. The four types 
of head in common usage are shown in Fig. 90. The dimensions 
for these screws may be obtained from any of the various 
machinists' hand-books. 

73. Foundation Bolts are used for fastening heavy machinery 
to the foundation. There are various forms, two of which are 
shown in Fig. 91. The Rag bolt is inserted into a conical shaped 
hole which is then filled with molten lead, thus permanently 
fastening the bolt in place. In the case of the Lewis bolt the 
holding key can be withdrawn and the bolt removed. 



CHAPTER VIII. 



Tracings and Prints. 

74. In general, the original pencil drawing does not leave the 
office but is kept on file for reference. The drawing is traced 
onto tracing cloth and from the tracing prints are made which 
are distributed as desired. The purpose of this chapter is to 
describe the details of this process. 

75. Tracings. — Tracing cloth is a fine grained fabric treated 
with a preparation consisting principally of starch in order to 
render it transparent and fit to receive ink lines. One side is 
highly polished and glazed and the reverse side is dull. Either 
side may be used, but most draftsmen prefer the dull side since 
it takes the ink more readily and permits of pencilled detailing 
as well. On the other hand it is harder to erase an ink line 
from the dull side. If the smooth side is used it should be dusted 
with powdered chalk and then wiped clean. The red selvage edge 
should be removed ana the tracing tacked tightly and smoothly 
over the drawing. This is best accomplished by first tacking 
diagonally opposite corners and then tacking the sides. 

The pencil lines of the drawing are easily visible through the 
tracing cloth and the ink lines of the tracing are drawn imme- 
diately over the pencil lines of the drawing. The lines are inked 
in the same general order as given in Art. 22. It should, however, 
be borne in mind that tracing cloth contracts or expands accord- 
ing to the state of the atmosphere, and hence had best be inked 
in sections so that no unfinished section will be left from one 
day to another. The invariable tendency of the novice is to 
make the ink lines too light. In order to insure good printing, 
the lines of a tracing should be heavier than would be required 
on a drawing. 

Dampness ruins tracing cloth and for this reason hands and 
bare arms should be kept off the cloth. 

In general lettered notes or titles or cross hatching should not 
be traced, but should be placed on the tracing as though it were 
original work. A scrap paper copy can be made of the lettering 



I04 MECHANICAL DRAWING 

and a sheet of white paper slipped under the tracing and over 
the lettering of the drawing. Then proceed with the lettering 
of the tracing without reference to the drawing. Traced letter- 
ing seldom looks well, especially if traced by one who did not 
letter the original drawing. 

Tracings may be cleaned by lightly rubbing with a cloth satu- 
rated with benzine or gasoline. 

Pen wipers may be obtained by soaking scrap pieces of tracing 
cloth in water until the starch is thoroughly removed. 

Tracing cloth is sold in 30" to 54" widths and in rolls from 10 
to 24 yards long. 

The tracing should never leave the office, the purpose of the 
tracing being to furnish prints as will be described in the next 
article. 

76. Prints. — The most common form of print is the so-called 
blue print. Blue prints are made by laying the tracing face 
up on a sheet of specially prepared sensitized paper, clamping the 
two tightly together and exposing to the sunlight or strong arti- 
ficial light. The light affects all of the sensitized paper except 
those parts covered by the ink lines of the tracing. The length 
of the exposure is dependent upon the degree of sensitiveness of 
the blue print paper and the strength of the light. The sensitized 
paper is then thoroughly washed in water and as a result white 
lines on a blue background are obtained. Such a print is called 
a blue print. 

By using specially prepared papers the following kinds of 
prints can be obtained, Vandyke Negatives (white lines on a 
brown background), Blue Line Prints (blue lines on a white 
background), and Black Line Prints (black lines on a white 
background). 

It is of interest to know that good prints can be made from 
typewritten matter provided a sheet of carbon paper was placed 
behind the page (carbon side next the paper) while doing the 
typewriting. 

In the next article will be described several types of machines 
used in making prints. 



TRACINGS AND PRINTS 



I05 



77. Sun Frames. — In Fig. 92 is shown a sun frame mounted on 
a truck to run on rails outside a window so that it may be fully 
exposed to the sunlight. The tracing is laid face down against 
the glass in the frame, the sensitized paper is then placed against 
the tracing and covered by a piece of felt in order to uniformly 
distribute the pressure, and the whole clamped into position by 
the back of the frame. The truck is then run into the sunlight 
and the frame revolved about a horizontal axis until the glass 
surface is exposed to the light. Prints may be made on a cloudy 
day by giving a longer exposure. The length of exposure 
depends not only upon the sensitiveness of the paper but on the 
strength of the light, and for any given combination is best ascer- 




Fig. 92. — Sun frame. 

tained by trial. Good prints cannot be made by this method on 
rainy days, and wherever much printing is done the sun method 
has been entirely supplanted by some form of electric printing 
machine as described in the next article. 

78. Electric Printing Machines may be divided into two classes, 
those in which the paper and the tracing remain stationary 
during the time of the exposure and which may therefore be 
called the stationary type of blue printing machine. In the 
second type of machine the sensitized paper and the tracing 
are moved before a light in such a manner that successive prints 
are made on the sensitized paper. This machine is a continuous 
printing machine. 

A Stationary Printing Machine of the vertical type is shown in 
Fig. 93. It consists essentially of a glass cylinder which is sup- 



io6 



MECHANICAL DRAWING 



ported on end in a suitable frame. An arc light is arranged so 
that it may be moved up and down through the center of the 
cylinder, the speed of the movement being controlled by a pendu- 
lum or other device. To operate this machine the tracing or 
tracings, from which the print is to be made, is placed next to 




Fig- 93- — Buckeye Vertical Electric Printing Machine. — Sold by Technical 
Supply Co., Scranton, Pa. 

the glass cylinder and the sensitized paper is held against the 
tracing by a curtain which is held tight by weights suitably 
arranged. The light having been raised, is then turned on and 
allowed to pass downward through the cylinder, the length of 
the speed regulating device having been so adjusted that one 
pass of the light will give the required length of exposure. 



TRACINGS AND PRINTS 



IC7 



These machines are built in various sizes, any one of which 
will make a number of small prints or one large one at a time, 
one pass of the light making the exposure in either case. An 
exposure on this machine takes from one and one-half to three 
minutes, depending upon the sensitiveness of the paper and the 
condition of the tracing. 

The Continuous Printing Machines are most successful when the 
surface on which the exposure is made is placed horizontally. 




Fig. 94. — Diagrammatic view of Everett-McAdams Continuous 
Printing Machine. 

They may be lighted by one or more arc lights or Cooper-Hewitt 
lights. The method of making the exposure differs somewhat, 
however, in different makes of the continuous printing machine. 
Fig. 94 is a diagrammatic end view of one of these machines. 
There is a glass cylinder which revolves around two Cooper- 
Hewitt lights placed near its center. The sensitized paper is 
passed around the cylinder to which it is held by the endless 



ioS 



MECHANICAL, DRAWING 



belts. The tracings from which prints are to be made, are fed 
between the sensitized paper and the glass cylinder. It is obvious 
that the speed of this machine must be such that one revolution 
of the cylinder takes the time required to make an exposure. 

A continuous printing machine that differs quite radically from 
the one just described is shown diagrammatically in Fig. 96. 




,Fig. 95.— Bverett-McAdams Continuous Printing Machine. — Sold by 
Technical Supply Co., Scranton, Pa. 

This machine uses two, three, or four Cooper-Hewitt lights 
shown at a. The glass plates over which the tracings and paper 
are passed while making the exposure are portions of a cylinder 
having a long radius. These glass plates are placed close to the 
lamps so that the full intensity of the light is concentrated on 
the printing surface. The tracings and sensitized paper are held 
against the glass plates by tension belts, d, each of which is 
driven independently of the other. It is therefore possible to 



TRACINGS AND PRINTS 



109 



make prints with two different kinds of sensitized paper at the 
same time even though the time of exposure may not be the same 
or, in case an extra long exposure is required, the print be passed 
first above the lights and then below them. This machine will 




Fig. 96. — Diagrammatic view of Continuous Printing Machine. 

print at the rate of from 1% to 12 feet per minute depending on 
the sensitiveness of the paper and the clearness of the tracing. 

A print washing attachment may be combined with a continu- 
ous printing machine but, owing to the fact that it is difficult to 
wash a print thoroughly as fast as it can be exposed, this 
arrangement does not promise very good results. 



APPENDIX. 



SUGGESTED COURSE IN MECHANICAL 
DRAWING. 



First Year Course in Drawing 
and Lettering. 



79. Time Devoted to Course. — The course in drawing extends 
throughout the Freshman year. During the first, second and 
third terms there are two two-hour drawing exercises per week, 
and during the second and third terms there are two one-hour 
recitations per week. Twenty-two plates are completed in this 
course. The course in lettering covers the first term, in which 
there are two one-hour exercises per week. Fifteen plates are 
made during the course. 

80. Roll Call. — A roll will be called immediately at the opening 
of each exercise, and a student arriving after this roll has been 
called will be marked tardy. Two such tardinesses, unless 
excused for special reasons by the instructor in charge, will be 
regarded as one absence, and reported as such. A second roll 
call will be taken five minutes before the close of each exercise, 
and any student who is not working at his own table at this time, 
will be regarded as having been absent the entire period. 

No preparations for leaving the drafting room should be made 
until after the conclusion of the final roll call. 

81. Stamping Plates. —As soon as the border lines of a plate 
are laid out in pencil, the student should ink his name, number, 
and plate number in their proper places. Before doing any fur- 
ther work on the plate see that an instructor stamps the plate 
with a form which states ''Started , Finished In- 
structor " and places the date after the word "Started." 

When the plate is completed do not remove same from the board 
until an instructor has placed the date of completion after "Fin- 
ished" and signed his initials after "Instructor." 

82. Posting of Accepted Plates. — On the bulletin board will be 
found- a form stating the names of the men taking each course 
and the number of plates in each course. Under each plate 
number is a date, which indicates the last day on which that par- 
ticular plate will be accepted with full credit. A plate handed 
in less than two weeks after that date will be given half credit and 



] 14 MECHANICAL DRAWING 

any plate more than two weeks overdue will be given a grade of 
zero in making up the final grade for the course. In this connec- 
tion due allowance will be made for permitted absences. 

A plate handed in during one exercise will be examined before 
the next exercise and if satisfactory an X will be placed opposite 
the name of the student and under the proper plate number. 

83. Plates Returned for Correction. — Any plate which is not 
acceptable, but that can be made so, is returned to the student 
for correction. Attached to the plate is a correction sheet on 
which are noted the necessary corrections. These changes are to 
be at once incorporated in the drawing, and both drawing and 
correction sheet returned at once to the office. The immediate 
correction of a plate should take precedence over any other work 
upon which the student may be engaged. 

84. Rejected Plates. — A plate will be rejected if the general 
character of its work is not up to the standard required by this 
department. The lower left hand corner of such a plate will be 
cut off and a correction sheet attached on which are noted the 
main reasons for the rejection of the plate. The rejected plate 
must be redrawn immediately after the completion of the plate 
upon which the student is then working, and the new plate handed 
in with the correction sheet attached. 

85. Time of Posting and Returning Plates. — At the next exer- 
cise following the handing in of a plate, the student should deter- 
mine from the list on the bulletin board whether or not the plate 
has been accepted. If the plate is not posted as accepted, it should 
be returned to the student, shortly after the opening of the exer- 
cise, as rejected or needing correction. If the plate is not 
accounted for in one of these ways, the matter should be called 
to the attention of the instructor in charge. 

86. Conduct in Drafting Room. — The general deportment of the 
student in this drafting room will be governed by the same prac- 
tical standards as effect the draftsman in professional drafting 
rooms. Brief conversation relative to the work in hand and 
carried on in a low tone of voice is permissible. 

Necessary movement about the room such as for the purpose 



FIRST YEAR COURSE IN DRAWING AND LETTERING 115 

of turning in a plate, consulting an instructor, examination of 
the model plates displayed on ♦the bulletin board, is permissible. 

Loud or unnecessary conversation, excessive movement about 
the room, or any manner of conduct which disturbs the others at 
work will not be tolerated. 

The good draftsman works quietly and steadily. The student 
should do likewise. 

Caps should be removed from the head before entering the 
room and not replaced until again outside. 

Equipment should be unpacked and packed with speed and 
quietness. 

87. Work Done Outside of Class Hours. — Under no condition is 
the drawing board to be removed from the drafting room. The 
student may work outside of the assigned class room hours, if he 
so desires, but such work must be done in the drafting room. 
Any work done on a plate outside of the drafting room, will be 
regarded as sufficient cause for rejecting the plate without further 
comment. 

88. Bulletin Boards. — On the bulletin boards are displayed 
plates whose excellence render them worthy models. Or it may 
be that these plates indicate more clearly than do the plates in 
the text-book certain details in construction. Notices pertaining 
to the courses are frequently posted, for the knowledge of which 
the student will be held responsible. It is, then, highly desirable 
that the student should watch the bulletin boards carefully. 

89. Size of Drawing Plates. — The over-all dimensions of the 
drawing plates are 12" x 18". A border line is drawn 1" from 
the top and bottom edges, 1^4" from the left hand edge and i*4" 
from the right hand edge, making the inside dimensions 10" x 15". 

From the lower right corner of the border draw a light pencil 
line to the same corner of the cutting edge. Bisect this line, and 
with this point as a center describe a circle having a radius of 
7 / m ". The circle should be drawn in ink, the width of line being 
somewhat heavier than a shade line. Draw in ink, but with a 
narrow line, a concentric circle just inside the outer circle leav- 
ing a hair space between the two circles. Draw lightly in pencil 



u6 



MECHANICAL DRAWING 



the horizontal diameter of these circles and %." above this diam- 
eter another pencilled horizontal line. Between these two guide 
lines print in black numerals the number assigned the individual 
student at the opening of the course. Just under the center of 
the horizontal diameter print in letters 3 /hb" high the course of 
study being pursued, using the following notation : 

Civil Engineering C. E. 

Mechanical Engineering M. E. 

Electrical Engineering E. E. 

Mining Engineering E. M. 

Chemistry C. 

General Scientific G. S. 

For an illustration of the foregoing data see Fig. 97. 



Sorc/erL/ne- 







A// p/afes fo Se 
/cr/af out /'/? accord- 
ance w/'th these d/men- 

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Fig. 97. — Layout of drawing plates. 

90. Instructions Regarding Each Plate are given under the 
proper plate numbers. These instructions should be read and 
noted before starting the construction of each plate. 



FIRST YEAR COURSE IN DRAWING AND LETTERING II7 

91. Binding Plates. — At the conclusion of each course the 
plates must be bound in bristol board covers, at a bindery 
approved by this department. The cost for binding the drawing 
plates is about thirty-five cents and for the lettering plates about 
twenty-five cents. Before credit will be given the students in 
either course the bound plates must be submitted to the instructor 
in charge. 



Plates. 



PLATE 1. 

Before starting work on this plate, study articles 7, 9, 20 
and 21. 

The purpose of this plate is to afford practice in the use of 
the right line pen, and to illustrate the character of lines used 
in mechanical drawing. 

Construct six 3%" squares leaving a space of y^" between each 
of the squares. The distance from the top border line to the top 
edges of the upper squares should be the same as the distance 
from the lower border line to the lowest edges of the under 
squares. Similarly the margin to the left of the squares should 
be equal to the margin at the right. It will be seen that the 
result of the foregoing work is two horizontal rows of squares, 
three J squares in each row. 

Divide the left hand edge of the first square in each row into 
thirty divisions of y&" each. By means of the T square carry 
these points of division into each of the remaining squares. It 
will be noted that up to this point the work has been in pencil, 
whereas the following lines are ruled directly in ink without pre- 
viously penciling them. 

Through the points of divisions in each of the squares rule 
horizontal lines of the following character; in the first square, 
dimension lines ; in the second square, visible outline lines ; in 
the third square invisible outline lines ; in the fourth square, cen- 
ter lines ; in the fifth square, shade lines ; and in the sixth square 
border lines which are one and one-half times as heavy as shade 
lines. (The squares are numbered horizontally from left to 
right.) 

Ink the border lines of each square using the same weight line 
as is included in each particular square. 

Under each square in lower case letters y$" high state the 
name of the lines included in that square. 



PLATES 110 



PLATE 2. 



Before starting work on this plate study Article n. 

The purpose of this plate is to afford practice in the use of tri- 
angles and in the accurate drawing of radiating lines. 

Set a point \Y%" from the left hand border line and 5" below 
the top border line. With this point as a center describe two 
concentric circles having diameters of 5" and Y^' , respectively. 
Draw radial lines 15 apart terminating in these circles. Con- 
nect the ends of the radial lines by straight lines, thus forming 
a large and a small polygon of twenty-four sides. Divide the 
left hand, horizontal radial line into eight equal parts. Through 
these points of division construct eight more concentric poly- 
gons. Carry the lines half way around in each direction from 
the points of division, in order to reduce the closing error of the 
polygons to a minimum. Ink the polygons before inking the 
radial lines. Do not ink the circles as they were used for con- 
struction only. 

Construct a 5" square the right hand side of which is i 1 /^' from 
the right hand border line, and which is equidistant from top and 
bottom border lines. Divide the left and right sides into ten 
equal parts. From the division points of one side draw lines 
to the center point of the opposite side. Ink the radiating lines 
before inking the sides of the square. One line should be al- 
lowed to thoroughly dry before inking the next one to it. Use 
great care to make the intersections at the centers clean-cut and 
free from the blur of unnecessary ink. 



J20 MECHANICAL DRAWING 



PLATE 3. 



Before starting work on this plate study Articles 3, 4 and 22. 

The purpose of this plate is to afford practice in the joining 
of straight lines to circular arcs, as well as to familiarize the 
student with the use of both large and small dividers and com- 
passes. 

The layout and construction of this plate are indicated in the 
illustration at the right. 

Wherever a straight line joins a circular arc, the arc should 
be first drawn and then the straight line drawn away from the 
arc. A smooth connection is essential to the good appearance 
of the work. 

The centers of the circles inclosed in the equilateral triangle 
are found by trial with the dividers. Before inking one of these 
circles swing the pen of the compass around the path of the de- 
sired circle and just above the plane of the paper so as to ascer- 
tain if the circle will be exactly tangent at the proper points. If 
necessary, slightly shift the center and make a slight change in 
radius so as to obtain the desired result. 

PLATE 4. 

Before starting work on this plate study Article 23. 

The purpose of this plate is to furnish practice in the drawing 
of lines of varying weights, and to illustrate symbolic cross 
hatching. 

Construct two horizontal rows of 2"x2^" rectangles, four 
rectangles in each row, the 2" side of the rectangles being paral- 
lel to the long side of the plate. Allow a space of \ l /\" between 
each rectangle and a space of ij4" between the two rows. The 
two rows are to be centered on the plate as regards the border 
lines. 

In these rectangles represent the following materials, by sym- 
bolic cross hatching, in the order here stated ; cast iron, wrought 
iron, cast steel, wrought steel, copper, brass, lead, and rubber. In 
each block state the name of the material represented using 
lower case letters 3-32" high. Do not cross hatch over the let- 
tering, but carry the lines as close to the letters as possible. All 



122 MECHANICAL DRAWING 

the section lines are to be drawn upward from left to right. Ink 
the section lines before inking the outline of the blocks. Shade 
the lower and right hand sides of each block. 

The common fault of placing the lines of the cross hatching 
too close together should be avoided. 

The section representing rubber (also vulcanite or any insu- 
lating material) is most easily made by ruling a series of heavy 
parallel lines in pairs, and filling in with ink the spaces between 
the adjacent pairs of lines. 

PLATE 5. 

The purpose of this plate is to afford an opportunity for gain- 
ing experience in the use of the free hand pen to illustrate vari- 
ous building materials. All lines on this plate are drawn free 
hand with the exception of the lines representing water. 

The same relative size of the various materials should be, in 
general, the same as shown in the accompanying illustration. 

The sand is composed of a great number of dots made with 
a free hand pen held almost vertically. Do not work too long 
at one spot as the ink of the individual blots will blur. Make a 
reasonable number of dots at one place, then move further along 
and return to the original place when the ink is dry. The dots 
should be very close together at the top and gradually become 
less towards the bottom. 

The concrete is composed of fine dots representing sand and 
cement through which are interspersed a number of small stones. 
Note that the stones are indicated by a shade line around the 
lower and right hand edges, no line being drawn for the upper 
and left hand sides. 

The uncoursed rubble is masonry composed of rough stones 
which have been rudely dressed by knocking off angular cor- 
ners. The stones are not laid in courses. 

The coursed rubble is brought to a horizontal course line every 
few feet. Care should be taken, in representing masonry of any 
character, not to show too much mortar. 

Earth and rock are represented by free hand parallel lines as 
shown ; in the illustration these lines are too close together. 



]24 MECHANICAL DRAWING 

PLATE 6. 

Before starting work on this plate study Articles 62 and 63. 

The purpose of this plate is to afford practice in the use of 
shade lines and line shading. 

The accompanying illustration consists of free hand sketches 
of various objects. These objects are to be accurately drawn 
to scale, though not necessarily in the same positions as here 
shown. Lay out all the pieces in pencil, before starting detail 
work on any piece, and submit the arrangement to an instructor 
for approval. After each piece is complete in pencil, apply the 
line shading and then ink the outline. 

Do not show the hole in the top view of the bearing block as it 
would tend to destroy the effect of the shading. 

State the name of each object but do not indicate the dimen- 
sions or scale. 

PLATE 7. 

Before starting work on this place study Articles 12, 33, 34, 
35, 36, 37 and 38. 

The purpose of this plate is to familiarize the student with 
the construction of the conic sections, as well as to afford prac- 
tice in the use of the irregular curve. 

The penciled layout of all the curves should be determined and 
submitted to an instructor for approval, before plotting the points 
of each curve. 

Construct an ellipse according to the second method of Arti- 
cle 36. Let the lengths of the major and minor axes be 4" and 
3", respectively; use twenty-four radial lines spaced entirely by 
means of the triangles. The weight of the radial lines when 
inked should be the same as for dimension lines. The ellipse, 
as well as all other curves on this plate, should be the same weight 
as for a shade line. Draw a tangent to any point on the curve. 

Construct an hyperbola, as explained in Article 38. Let 
FF X — 2^4" and VV a = 2%.". Plot a sufficient number of 
points to draw each branch of the curve with accuracy. Draw 
tangents from a point outside the curve and at a point on the 



126 MECHANICAL DRAWING 

curve. Ink the construction lines used in obtaining one point 
only, on each of the branches of the curve. 

Construct a parabola according to the second method of Arti- 
cle 37. Let the rectangle in which the parabola is enclosed be a 
4" square. Plot a sufficient number of points to draw the curve 
accurately. 

Construct a parabola according to the first method of Article 
37. Let F be distant £4" from the directrix. Let the last point 
chosen on the axis be 3^2" from the directrix. Draw tangents 
from a point outside the curve and also at a point on the curve. 

In each of the foregoing constructions letter the axis, direc- 
trix, foci, and vertex. State the name of each curve in capitals 

H" high. 

PLATES 8 and 9. 

Orthographic Projection of Geometric Objects. 

A thorough understanding of the chapter on orthographic pro- 
jection is essential to the correct solutions of the problems on 
these plates. 

Divide each of these plates into six 5"x5" squares by light 
pencil lines. 

Plates 8 and 9 each consist of six problems assigned by the in- 
structor from the following list of problems as stated on page — : 
ia, ib, ic, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b, 6c, 
7a, 7b, 7c, 8a, 8b, 8c, 9, 10a, 10b, 10c, 11a, lib, 11c, 12a, 12b and 
12c. 

Completely solve each problem in pencil before starting the 
inking. Ink the outlines of the various views, but do not ink the 
ground line, profile plane trace, or the projecting lines. Erase 
the pencil lines used to divide the plate into six equal parts. 

PLATES 10 and 11. 
Revolution of Geometric Objects. 

A thorough knowledge of the chapter on orthographic projec- 
tion is essential to the correct solutions of the problems on these 
plates. 

Divide each plate into four 5"x7^2" rectangles by light pencil 
lines. 



PLATES 127 

Plates 11 and 12 each consist of one problem assigned by the 
instructor from the following list of problems as stated on page 
— : 25, 26, 27, 28, 29 and 30. 

Complete each problem in pencil before starting the inking. 
Ink only the outlines of the various views. 

PLATES 12 and 13. 
Successive Revolution of Geometric Objects. 

A thorough knowledge of the chapter on orthographic pro- 
jection is essential to the correct solutions of the problems on 
these plates. 

Divide each plate into four 5"x7^" rectangles by light pencil 
lines. 

Plates 12 and 13 each consist of one problem assigned by the 
instructor from the following list of problems as stated on page 
— : 3i, 32, 33, 34, 35, 3^, 37 and 38. 

Complete each problem in pencil before starting the inking. 
Ink only the outlines of the various views. . 

PLATE 14. 
Auxiliary Views. 

A thorough knowledge of the chapter on orthographic pro- 
jection is essential to the correct solutions of the problems on this 
plate. ' 

Divide the plate into four 5"x7^" rectangles by light pencil 
lines. 

This plate consists of four problems assigned by the instruc- 
tor from the following list of problems as stated on page — : 
39a. 39b, 39c, 39d and 39c 

Complete each problem in pencil before starting the inking. 
Ink only the outlines of the various views. 

PLATE 15. 

Machine Details. 

A thorough knowledge of the chapters on orthographic pro- 
jection and working drawings is essential to the correct solutions 
of the problems on this plate. 

Divide the plate into six 5"x5" squares by light pencil lines. 



128 MECHANICAL DRAWING 

This plate consists of six problems assigned by the instructor 
from the following list of problems as stated on page — : 13, 
14, 15, 16, 17, 18, 19, 20, 21, 22, 23 and 24. 

In drawing these objects do not use the ground line or profile 
plane trace. If, in the opinion of the student, any view other 
than those called for in these problems will better illustrate the 
object in question, the student is at liberty to pencil the proposed 
view and submit same to an instructor for approval or condem- 
nation. 

Complete each problem in pencil before starting the inking. 

PLATE 16. 

Before starting work on this plate study Articles 66, 67, 68 
and 69. 

This plate consists of the following drawings of bolt heads 
and nuts, and screw threads : 

Application of the helix to a single square thread of 1" pitch 
and 3" diameter similar to the one shown in Fig. 84. The 
thread is to be 3/^" long the lower part being shown in section. 
The thread is to be shown upright at the extreme left of the 
plate. 

Rounded hexagonal head and nut, across corners. 

Chamfered hexagonal head and nut, across flats. 

Chamfered square head and nut, across corners. 

Chamfered square head and nut across flats. 

Two conventional representations — the style to be assigned by 
the instructor — of a single V thread, diameter i^i", 6 threads 
per inch. 

One conventional representation of a double V thread, diame- 
ter i}i". 

One conventional representation of a double square thread, 

pitch y 2 ". 

Each thread is to be 3" long. 



PLATES 129 

The heads and nuts are to fit a bolt having a diameter of i}i", 
I/4", or 1^4" as assigned by the instructor. In the case of a nut 
show the bolt broken on each side of the nut; for the head the 
bolt is shown on one side only. 

The pencil layout of the various pieces, showing over all di- 
mensions only, should be determined and submitted to an in- 
structor for approval before detailing any view. 

Draw threads directly in ink without previously pencilling 
them. 

State the names of the various pieces in lower case letters 

TJ 

3 / 16 " high ; also state the value of D, H, and — . 

Dimension the heads and nuts in terms of D. 
In the lower right hand corner of the plate state in capital let- 
ters 3 / 16 " high, "Standard Nuts, Heads and Screw Threads." 



130 MECHANICAL DRAWING 



PLATE 17. 

The accompanying illustration shows free hand sketches of 
various washers and fastenings. From these sketches the stu- 
dent is to make accurate working drawings. 

In addition to the views shown in the illustration show a top 
view of the Cup and Ogee Washers, Separator, Boat Spike, and 
Drift Bolts. 

Draw all pieces half size except the Dowel and Boat Spike 
which are to be drawn full size. 

Lay out the over all dimensions of each view and submit the 
arrangement to an instructor for approval before detailing any 
view. 

Use shade lines on all views, and represent convex or concave 
surfaces by line shading except in the case of screw threads. 

In some of the sketches the word "round" is placed after a di- 
mension representing the diameter of a circular piece. When 
the top view is shown the word is omitted. 

Some of the fastenings shown on this plate are used in the 
construction of the timber trestle represented on the following 
plate. 



132 MECHANICAL DRAWING 



PLATE 18. 

In the accompanying illustration are shown the details of a 
single deck bent for a squared timber trestle. From these de- 
tails the student is to draw the complete bent to a scale of y 2 " — 
1'— o". 

The small drawing in the lower left hand corner shows the 
general form of the completed bent, and is not to be placed on 
the drawing made by the student. 

Some of the fastenings enumerated in the note at the left are 
not shown in the details, but should be shown by the student as 
stated in the note. Some of the fastenings are shown in detail 
on Plate 17. 

Use shade lines. 



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134 MECHANICAL DRAWING 



PLATE 19. 

The accompanying illustration is an uncompleted drawing of 
a squared timber highway bridge. From the data given the stu- 
dent is to make a complete drawing of this bridge to a scale of 
i" = i'— o". 

Both the side and end views of all timbers are to be grained. 
The success of the graining is largely dependent upon the artis- 
tic ability of the student. Any arrangement of lines which gives 
a formal or mechanical appearance should be carefully avoided. 
Examine Fig. 31, obtain personal instruction, and devote a few 
minutes to practice before starting the graining. One result of 
the graining should be to make adjoining timbers stand out 
clearly. 

After the drawing is completely inked and shade lined, apply 
the following light washes of color : 

To all wood, "Light Wood." 

To all iron work, "Prussian Blue." 

To all masonry, "Prussian Blue," somewhat lighter than for 
iron. 

To earth, one part of "Gamboge," two parts of "Light Wood," 
and a touch of India Ink. 

To water, "Prussian Blue" dark at the surface and growing 
gradually lighter towards the bottom. 

The common fault of the amateur to make all the colors too 
heavy should be avoided. Submit the washes to an instructor 
before applying. 



136 



MECHANICAL DRAWING 



PLATE 20. 

Before starting work on this plate study Article 64. 
This plate consists of three drawings as follows : 
Two views of the Z Bar column shown in Fig. 98. 



Z ANGLES 3 f'3i*. 



RIVETS §D. 



WEB PLATE 8*j 




Fig. 98.— Z-Bar Column. 

Two views of the Angle column whose cross section is shown 
in the accompanying illustration. 

Two views of the Girder whose front view is shown in the ac- 
companying illustration. 

The scale in each case is to be ij4" = i' — o". 

Layout the over all dimensions of the various views and sub- 
mit the arrangement to an instructor before detailing any view. 

Locate the center lines of the rivets in pencil, but draw the 
rivets directly in ink. 

Do not use shade lines on this plate. 



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PLATE 21. 

Before starting work on this plate study Article 75. 
This plate consists of a tracing made from one of the follow- 
ing plates as assigned by instructor: 6, 15, 16, 17, 18, 19 and 20. 

PLATE 22. 

Plate 22 is the title plate. The lettering consists of block let- 
ters similar to those shown on Plate VI of "Freehand Letter- 
ing" — Reinhardt, or similar to a model plate posted for this pur- 
pose by the instructor. 

In capital letters 5/ 8 " high state "MECHANICAL DRAW- 
ING." Underneath and distant 1" state in capital letters 7 / 16 " 
high the name of the College. Below this line 7 / 1G " state in lower 
case letters 3 / 16 " high the name of the department in which the 
course was pursued, as "Department of Graphics ;" the D and 
G in capitals 5 / 10 " high. 

In the lower left hand corner of the plate in Reinhardt lower 
case letters ]/%" high, state "Freshman Class 191- to 191-." 

In the lower right hand corner state name, date and number 
as usual. 



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